GREP Command
Search for the given string in a single file
The basic usage of grep command is to search for a specific string in the specified file as shown below.
Syntax:
grep "literal_string" filename
$ grep "this" demo_file
this line is the 1st lower case line in this file.
Two lines above this line is empty.
And this is the last line.
2. Checking for the given string in multiple files.
Syntax:
grep "string" FILE_PATTERN
This is also a basic usage of grep command. For this example, let us copy the demo_file to demo_file1. The grep output will also include the file name in front of the line that matched the specific pattern as shown below. When the Linux shell sees the meta character, it does the expansion and gives all the files as input to grep.
$ cp demo_file demo_file1
$ grep "this" demo_*
demo_file:this line is the 1st lower case line in this file.
demo_file:Two lines above this line is empty.
demo_file:And this is the last line.
demo_file1:this line is the 1st lower case line in this file.
demo_file1:Two lines above this line is empty.
demo_file1:And this is the last line.
3. Case insensitive search using grep -i
Syntax:
grep -i "string" FILE
This is also a basic usage of the grep. This searches for the given string/pattern case insensitively. So it matches all the words such as “the”, “THE” and “The” case insensitively as shown below.
$ grep -i "the" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE.
this line is the 1st lower case line in this file.
This Line Has All Its First Character Of The Word With Upper Case.
And this is the last line.
4. Match regular expression in files
Syntax:
grep "REGEX" filename
This is a very powerful feature, if you can use use regular expression effectively. In the following example, it searches for all the pattern that starts with “lines” and ends with “empty” with anything in-between. i.e To search “lines[anything in-between]empty” in the demo_file.
$ grep "lines.*empty" demo_file
Two lines above this line is empty.
From documentation of grep: A regular expression may be followed by one of several repetition operators:
• ? The preceding item is optional and matched at most once.
• * The preceding item will be matched zero or more times.
• + The preceding item will be matched one or more times.
• {n} The preceding item is matched exactly n times.
• {n,} The preceding item is matched n or more times.
• {,m} The preceding item is matched at most m times.
• {n,m} The preceding item is matched at least n times, but not more than m times.
5. Checking for full words, not for sub-strings using grep -w
If you want to search for a word, and to avoid it to match the substrings use -w option. Just doing out a normal search will show out all the lines.
The following example is the regular grep where it is searching for “is”. When you search for “is”, without any option it will show out “is”, “his”, “this” and everything which has the substring “is”.
$ grep -i "is" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE.
this line is the 1st lower case line in this file.
This Line Has All Its First Character Of The Word With Upper Case.
Two lines above this line is empty.
And this is the last line.
The following example is the WORD grep where it is searching only for the word “is”. Please note that this output does not contain the line “This Line Has All Its First Character Of The Word With Upper Case”, even though “is” is there in the “This”, as the following is looking only for the word “is” and not for “this”.
$ grep -iw "is" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE.
this line is the 1st lower case line in this file.
Two lines above this line is empty.
And this is the last line.
6. Displaying lines before/after/around the match using grep -A, -B and -C
When doing a grep on a huge file, it may be useful to see some lines after the match. You might feel handy if grep can show you not only the matching lines but also the lines after/before/around the match.
Please create the following demo_text file for this example.
$ cat demo_text
4. Vim Word Navigation
You may want to do several navigation in relation to the words, such as:
* e - go to the end of the current word.
* E - go to the end of the current WORD.
* b - go to the previous (before) word.
* B - go to the previous (before) WORD.
* w - go to the next word.
* W - go to the next WORD.
WORD - WORD consists of a sequence of non-blank characters, separated with white space.
word - word consists of a sequence of letters, digits and underscores.
Example to show the difference between WORD and word
* 192.168.1.1 - single WORD
* 192.168.1.1 - seven words.
6.1 Display N lines after match
-A is the option which prints the specified N lines after the match as shown below.
Syntax:
grep -A "string" FILENAME
The following example prints the matched line, along with the 3 lines after it.
$ grep -A 3 -i "example" demo_text
Example to show the difference between WORD and word
* 192.168.1.1 - single WORD
* 192.168.1.1 - seven words.
6.2 Display N lines before match
-B is the option which prints the specified N lines before the match.
Syntax:
grep -B "string" FILENAME
When you had option to show the N lines after match, you have the -B option for the opposite.
$ grep -B 2 "single WORD" demo_text
Example to show the difference between WORD and word
* 192.168.1.1 - single WORD
6.3 Display N lines around match
-C is the option which prints the specified N lines before the match. In some occasion you might want the match to be appeared with the lines from both the side. This options shows N lines in both the side(before & after) of match.
$ grep -C 2 "Example" demo_text
word - word consists of a sequence of letters, digits and underscores.
Example to show the difference between WORD and word
* 192.168.1.1 - single WORD
7. Highlighting the search using GREP_OPTIONS
As grep prints out lines from the file by the pattern / string you had given, if you wanted it to highlight which part matches the line, then you need to follow the following way.
When you do the following export you will get the highlighting of the matched searches. In the following example, it will highlight all the this when you set the GREP_OPTIONS environment variable as shown below.
$ export GREP_OPTIONS='--color=auto' GREP_COLOR='100;8'
$ grep this demo_file
this line is the 1st lower case line in this file.
Two lines above this line is empty.
And this is the last line.
8. Searching in all files recursively using grep -r
When you want to search in all the files under the current directory and its sub directory. -r option is the one which you need to use. The following example will look for the string “ramesh” in all the files in the current directory and all it’s subdirectory.
$ grep -r "ramesh" *
9. Invert match using grep -v
You had different options to show the lines matched, to show the lines before match, and to show the lines after match, and to highlight match. So definitely You’d also want the option -v to do invert match.
When you want to display the lines which does not matches the given string/pattern, use the option -v as shown below. This example will display all the lines that did not match the word “go”.
$ grep -v "go" demo_text
4. Vim Word Navigation
You may want to do several navigation in relation to the words, such as:
WORD - WORD consists of a sequence of non-blank characters, separated with white space.
word - word consists of a sequence of letters, digits and underscores.
Example to show the difference between WORD and word
* 192.168.1.1 - single WORD
* 192.168.1.1 - seven words.
10. display the lines which does not matches all the given pattern.
Syntax:
grep -v -e "pattern" -e "pattern"
$ cat test-file.txt
a
b
c
d
$ grep -v -e "a" -e "b" -e "c" test-file.txt
d
11. Counting the number of matches using grep -c
When you want to count that how many lines matches the given pattern/string, then use the option -c.
Syntax:
grep -c "pattern" filename
$ grep -c "go" demo_text
6
When you want do find out how many lines matches the pattern
$ grep -c this demo_file
3
When you want do find out how many lines that does not match the pattern
$ grep -v -c this demo_file
4
12. Display only the file names which matches the given pattern using grep -l
If you want the grep to show out only the file names which matched the given pattern, use the -l (lower-case L) option.
When you give multiple files to the grep as input, it displays the names of file which contains the text that matches the pattern, will be very handy when you try to find some notes in your whole directory structure.
$ grep -l this demo_*
demo_file
demo_file1
13. Show only the matched string
By default grep will show the line which matches the given pattern/string, but if you want the grep to show out only the matched string of the pattern then use the -o option.
It might not be that much useful when you give the string straight forward. But it becomes very useful when you give a regex pattern and trying to see what it matches as
$ grep -o "is.*line" demo_file
is line is the 1st lower case line
is line
is is the last line
14. Show the position of match in the line
When you want grep to show the position where it matches the pattern in the file, use the following options as
Syntax:
grep -o -b "pattern" file
$ cat temp-file.txt
12345
12345
$ grep -o -b "3" temp-file.txt
2:3
8:3
Note: The output of the grep command above is not the position in the line, it is byte offset of the whole file.
15. Show line number while displaying the output using grep -n
To show the line number of file with the line matched. It does 1-based line numbering for each file. Use -n option to utilize this feature.
$ grep -n "go" demo_text
5: * e - go to the end of the current word.
6: * E - go to the end of the current WORD.
7: * b - go to the previous (before) word.
8: * B - go to the previous (before) WORD.
9: * w - go to the next word.
10: * W - go to the next WORD.
Cut Command in Unix ( Linux) Examples
Cut command in unix (or linux) is used to select sections of text from each line of files. You can use the cut command to select fields or columns from a line by specifying a delimiter or you can select a portion of text by specifying the range or characters. Basically the cut command slices a line and extracts the text.
Unix Cut Command Example
We will see the usage of cut command by considering the below text file as an example
> cat file.txt
unix or linux os
is unix good os
is linux good os
1. Write a unix/linux cut command to print characters by position?
The cut command can be used to print characters in a line by specifying the position of the characters. To print the characters in a line, use the -c option in cut command
cut -c4 file.txt
x
u
l
The above cut command prints the fourth character in each line of the file. You can print more than one character at a time by specifying the character positions in a comma separated list as shown in the below example
cut -c4,6 file.txt
xo
ui
ln
This command prints the fourth and sixth character in each line.
2.Write a unix/linux cut command to print characters by range?
You can print a range of characters in a line by specifying the start and end position of the characters.
cut -c4-7 file.txt
x or
unix
linu
The above cut command prints the characters from fourth position to the seventh position in each line. To print the first six characters in a line, omit the start position and specify only the end position.
cut -c-6 file.txt
unix o
is uni
is lin
To print the characters from tenth position to the end, specify only the start position and omit the end position.
cut -c10- file.txt
inux os
ood os
good os
If you omit the start and end positions, then the cut command prints the entire line.
cut -c- file.txt
3.Write a unix/linux cut command to print the fields using the delimiter?
You can use the cut command just as awk command to extract the fields in a file using a delimiter. The -d option in cut command can be used to specify the delimiter and -f option is used to specify the field position.
cut -d' ' -f2 file.txt
or
unix
linux
This command prints the second field in each line by treating the space as delimiter. You can print more than one field by specifying the position of the fields in a comma delimited list.
cut -d' ' -f2,3 file.txt
or linux
unix good
linux good
The above command prints the second and third field in each line.
Note: If the delimiter you specified is not exists in the line, then the cut command prints the entire line. To suppress these lines use the -s option in cut command.
4. Write a unix/linux cut command to display range of fields?
You can print a range of fields by specifying the start and end position.
cut -d' ' -f1-3 file.txt
The above command prints the first, second and third fields. To print the first three fields, you can ignore the start position and specify only the end position.
cut -d' ' -f-3 file.txt
To print the fields from second fields to last field, you can omit the last field position.
cut -d' ' -f2- file.txt
5. Write a unix/linux cut command to display the first field from /etc/passwd file?
The /etc/passwd is a delimited file and the delimiter is a colon (:). The cut command to display the first field in /etc/passwd file is
cut -d':' -f1 /etc/passwd
6. The input file contains the below text
> cat filenames.txt
logfile.dat
sum.pl
add_int.sh
Using the cut command extract the portion after the dot.
First reverse the text in each line and then apply the command on it.
rev filenames.txt | cut -d'.' -f1
Sed Command in Unix and Linux Examples
Sed is a Stream Editor used for modifying the files in unix (or linux). Whenever you want to make changes to the file automatically, sed comes in handy to do this. Most people never learn its power; they just simply use sed to replace text. You can do many things apart from replacing text with sed. Here I will describe the features of sed with examples.
Consider the below text file as an input.
>cat file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
unixlinux which one you choose.
Sed Command Examples
1. Replacing or substituting string
Sed command is mostly used to replace the text in a file. The below simple sed command replaces the word "unix" with "linux" in the file.
>sed 's/unix/linux/' file.txt
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.
Here the "s" specifies the substitution operation. The "/" are delimiters. The "unix" is the search pattern and the "linux" is the replacement string.
By default, the sed command replaces the first occurrence of the pattern in each line and it won't replace the second, third...occurrence in the line.
2. Replacing the nth occurrence of a pattern in a line.
Use the /1, /2 etc flags to replace the first, second occurrence of a pattern in a line. The below command replaces the second occurrence of the word "unix" with "linux" in a line.
>sed 's/unix/linux/2' file.txt
unix is great os. linux is opensource. unix is free os.
learn operating system.
unixlinux which one you choose.
3. Replacing all the occurrence of the pattern in a line.
The substitute flag /g (global replacement) specifies the sed command to replace all the occurrences of the string in the line.
>sed 's/unix/linux/g' file.txt
linux is great os. linux is opensource. linux is free os.
learn operating system.
linuxlinux which one you choose.
4. Replacing from nth occurrence to all occurrences in a line.
Use the combination of /1, /2 etc and /g to replace all the patterns from the nth occurrence of a pattern in a line. The following sed command replaces the third, fourth, fifth... "unix" word with "linux" word in a line.
>sed 's/unix/linux/3g' file.txt
unix is great os. unix is opensource. linux is free os.
learn operating system.
unixlinux which one you choose.
5. Changing the slash (/) delimiter
You can use any delimiter other than the slash. As an example if you want to change the web url to another url as
>sed 's/http:\/\//www/' file.txt
In this case the url consists the delimiter character which we used. In that case you have to escape the slash with backslash character, otherwise the substitution won't work.
Using too many backslashes makes the sed command look awkward. In this case we can change the delimiter to another character as shown in the below example.
>sed 's_http://_www_' file.txt
>sed 's|http://|www|' file.txt
6. Using & as the matched string
There might be cases where you want to search for the pattern and replace that pattern by adding some extra characters to it. In such cases & comes in handy. The & represents the matched string.
>sed 's/unix/{&}/' file.txt
{unix} is great os. unix is opensource. unix is free os.
learn operating system.
{unix}linux which one you choose.
>sed 's/unix/{&&}/' file.txt
{unixunix} is great os. unix is opensource. unix is free os.
learn operating system.
{unixunix}linux which one you choose.
7. Using \1,\2 and so on to \9
The first pair of parenthesis specified in the pattern represents the \1, the second represents the \2 and so on. The \1,\2 can be used in the replacement string to make changes to the source string. As an example, if you want to replace the word "unix" in a line with twice as the word like "unixunix" use the sed command as below.
>sed 's/\(unix\)/\1\1/' file.txt
unixunix is great os. unix is opensource. unix is free os.
learn operating system.
unixunixlinux which one you choose.
The parenthesis needs to be escaped with the backslash character. Another example is if you want to switch the words "unixlinux" as "linuxunix", the sed command is
>sed 's/\(unix\)\(linux\)/\2\1/' file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
linuxunix which one you choose.
Another example is switching the first three characters in a line
>sed 's/^\(.\)\(.\)\(.\)/\3\2\1/' file.txt
inux is great os. unix is opensource. unix is free os.
aelrn operating system.
inuxlinux which one you choose.
8. Duplicating the replaced line with /p flag
The /p print flag prints the replaced line twice on the terminal. If a line does not have the search pattern and is not replaced, then the /p prints that line only once.
>sed 's/unix/linux/p' file.txt
linux is great os. unix is opensource. unix is free os.
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.
linuxlinux which one you choose.
9. Printing only the replaced lines
Use the -n option along with the /p print flag to display only the replaced lines. Here the -n option suppresses the duplicate rows generated by the /p flag and prints the replaced lines only one time.
>sed -n 's/unix/linux/p' file.txt
linux is great os. unix is opensource. unix is free os.
linuxlinux which one you choose.
If you use -n alone without /p, then the sed does not print anything.
10. Running multiple sed commands.
You can run multiple sed commands by piping the output of one sed command as input to another sed command.
>sed 's/unix/linux/' file.txt| sed 's/os/system/'
linux is great system. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you chosysteme.
Sed provides -e option to run multiple sed commands in a single sed command. The above output can be achieved in a single sed command as shown below.
>sed -e 's/unix/linux/' -e 's/os/system/' file.txt
linux is great system. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you chosysteme.
11. Replacing string on a specific line number.
You can restrict the sed command to replace the string on a specific line number. An example is
>sed '3 s/unix/linux/' file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.
The above sed command replaces the string only on the third line.
12. Replacing string on a range of lines.
You can specify a range of line numbers to the sed command for replacing a string.
>sed '1,3 s/unix/linux/' file.txt
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.
Here the sed command replaces the lines with range from 1 to 3. Another example is
>sed '2,$ s/unix/linux/' file.txt
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.
Here $ indicates the last line in the file. So the sed command replaces the text from second line to last line in the file.
13. Replace on a lines which matches a pattern.
You can specify a pattern to the sed command to match in a line. If the pattern match occurs, then only the sed command looks for the string to be replaced and if it finds, then the sed command replaces the string.
>sed '/linux/ s/unix/centos/' file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
centoslinux which one you choose.
Here the sed command first looks for the lines which has the pattern "linux" and then replaces the word "unix" with "centos".
14. Deleting lines.
You can delete the lines a file by specifying the line number or a range or numbers.
>sed '2 d' file.txt
>sed '5,$ d' file.txt
15. Duplicating lines
You can make the sed command to print each line of a file two times.
>sed 'p' file.txt
16. Sed as grep command
You can make sed command to work as similar to grep command.
>grep 'unix' file.txt
>sed -n '/unix/ p' file.txt
Here the sed command looks for the pattern "unix" in each line of a file and prints those lines that has the pattern.
You can also make the sed command to work as grep -v, just by using the reversing the sed with NOT (!).
>grep -v 'unix' file.txt
>sed -n '/unix/ !p' file.txt
The ! here inverts the pattern match.
17. Add a line after a match.
The sed command can add a new line after a pattern match is found. The "a" command to sed tells it to add a new line after a match is found.
>sed '/unix/ a "Add a new line"' file.txt
unix is great os. unix is opensource. unix is free os.
"Add a new line"
learn operating system.
unixlinux which one you choose.
"Add a new line"
18. Add a line before a match
The sed command can add a new line before a pattern match is found. The "i" command to sed tells it to add a new line before a match is found.
>sed '/unix/ i "Add a new line"' file.txt
"Add a new line"
unix is great os. unix is opensource. unix is free os.
learn operating system.
"Add a new line"
unixlinux which one you choose.
19. Change a line
The sed command can be used to replace an entire line with a new line. The "c" command to sed tells it to change the line.
>sed '/unix/ c "Change line"' file.txt
"Change line"
learn operating system.
"Change line"
20. Transform like tr command
The sed command can be used to convert the lower case letters to upper case letters by using the transform "y" option.
>sed 'y/ul/UL/' file.txt
Unix is great os. Unix is opensoUrce. Unix is free os.
Learn operating system.
UnixLinUx which one yoU choose.
Here the sed command transforms the alphabets "ul" into their uppercase format "UL"
. Display timestamp using HISTTIMEFORMAT
Typically when you type history from command line, it displays the command# and the command. For auditing purpose, it may be beneficial to display the timepstamp along with the command as shown below.
# export HISTTIMEFORMAT='%F %T '
# history | more
1 2008-08-05 19:02:39 service network restart
2 2008-08-05 19:02:39 exit
3 2008-08-05 19:02:39 id
4 2008-08-05 19:02:39 cat /etc/redhat-release
2. Search the history using Control+R
I strongly believe, this may be your most frequently used feature of history. When you’ve already executed a very long command, you can simply search history using a keyword and re-execute the same command without having to type it fully. Press Control+R and type the keyword. In the following example, I searched for red, which displayed the previous command “cat /etc/redhat-release” in the history that contained the word red.
# [Press Ctrl+R from the command prompt,
which will display the reverse-i-search prompt]
(reverse-i-search)`red': cat /etc/redhat-release
[Note: Press enter when you see your command,
which will execute the command from the history]
# cat /etc/redhat-release
Fedora release 9 (Sulphur)
Sometimes you want to edit a command from history before executing it. For e.g. you can search for httpd, which will display service httpd stop from the command history, select this command and change the stop to start and re-execute it again as shown below.
# [Press Ctrl+R from the command prompt,
which will display the reverse-i-search prompt]
(reverse-i-search)`httpd': service httpd stop
[Note: Press either left arrow or right arrow key when you see your
command, which will display the command for you to edit, before executing it]
# service httpd start
3. Repeat previous command quickly using 4 different methods
Sometime you may end up repeating the previous commands for various reasons. Following are the 4 different ways to repeat the last executed command.
1. Use the up arrow to view the previous command and press enter to execute it.
2. Type !! and press enter from the command line
3. Type !-1 and press enter from the command line.
4. Press Control+P will display the previous command, press enter to execute it
4. Execute a specific command from history
In the following example, If you want to repeat the command #4, you can do !4 as shown below.
# history | more
1 service network restart
2 exit
3 id
4 cat /etc/redhat-release
# !4
cat /etc/redhat-release
Fedora release 9 (Sulphur)
5. Execute previous command that starts with a specific word
Type ! followed by the starting few letters of the command that you would like to re-execute. In the following example, typing !ps and enter, executed the previous command starting with ps, which is ‘ps aux | grep yp’.
# !ps
ps aux | grep yp
root 16947 0.0 0.1 36516 1264 ? Sl 13:10 0:00 ypbind
root 17503 0.0 0.0 4124 740 pts/0 S+ 19:19 0:00 grep yp
6. Control the total number of lines in the history using HISTSIZE
Append the following two lines to the .bash_profile and relogin to the bash shell again to see the change. In this example, only 450 command will be stored in the bash history.
# vi ~/.bash_profile
HISTSIZE=450
HISTFILESIZE=450
7. Change the history file name using HISTFILE
By default, history is stored in ~/.bash_history file. Add the following line to the .bash_profile and relogin to the bash shell, to store the history command in .commandline_warrior file instead of .bash_history file. I’m yet to figure out a practical use for this. I can see this getting used when you want to track commands executed from different terminals using different history file name.
# vi ~/.bash_profile
HISTFILE=/root/.commandline_warrior
If you have a good reason to change the name of the history file, please share it with me, as I’m interested in finding out how you are using this feature.
8. Eliminate the continuous repeated entry from history using HISTCONTROL
In the following example pwd was typed three times, when you do history, you can see all the 3 continuous occurrences of it. To eliminate duplicates, set HISTCONTROL to ignoredups as shown below.
# pwd
# pwd
# pwd
# history | tail -4
44 pwd
45 pwd
46 pwd [Note that there are three pwd commands in history, after
executing pwd 3 times as shown above]
47 history | tail -4
# export HISTCONTROL=ignoredups
# pwd
# pwd
# pwd
# history | tail -3
56 export HISTCONTROL=ignoredups
57 pwd [Note that there is only one pwd command in the history, even after
executing pwd 3 times as shown above]
58 history | tail -4
9. Erase duplicates across the whole history using HISTCONTROL
The ignoredups shown above removes duplicates only if they are consecutive commands. To eliminate duplicates across the whole history, set the HISTCONTROL to erasedups as shown below.
# export HISTCONTROL=erasedups
# pwd
# service httpd stop
# history | tail -3
38 pwd
39 service httpd stop
40 history | tail -3
# ls -ltr
# service httpd stop
# history | tail -6
35 export HISTCONTROL=erasedups
36 pwd
37 history | tail -3
38 ls -ltr
39 service httpd stop
[Note that the previous service httpd stop after pwd got erased]
40 history | tail -6
10. Force history not to remember a particular command using HISTCONTROL
When you execute a command, you can instruct history to ignore the command by setting HISTCONTROL to ignorespace AND typing a space in front of the command as shown below. I can see lot of junior sysadmins getting excited about this, as they can hide a command from the history. It is good to understand how ignorespace works. But, as a best practice, don’t hide purposefully anything from history.
# export HISTCONTROL=ignorespace
# ls -ltr
# pwd
# service httpd stop [Note that there is a space at the beginning of service,
to ignore this command from history]
# history | tail -3
67 ls -ltr
68 pwd
69 history | tail -3
11. Clear all the previous history using option -c
Sometime you may want to clear all the previous history, but want to keep the history moving forward.
# history -c
12. Subtitute words from history commands
When you are searching through history, you may want to execute a different command but use the same parameter from the command that you’ve just searched.
In the example below, the !!:$ next to the vi command gets the argument from the previous command to the current command.
# ls anaconda-ks.cfg
anaconda-ks.cfg
# vi !!:$
vi anaconda-ks.cfg
In the example below, the !^ next to the vi command gets the first argument from the previous command (i.e cp command) to the current command (i.e vi command).
# cp anaconda-ks.cfg anaconda-ks.cfg.bak
anaconda-ks.cfg
# vi !^
vi anaconda-ks.cfg
13. Substitute a specific argument for a specific command.
In the example below, !cp:2 searches for the previous command in history that starts with cp and takes the second argument of cp and substitutes it for the ls -l command as shown below.
# cp ~/longname.txt /really/a/very/long/path/long-filename.txt
# ls -l !cp:2
ls -l /really/a/very/long/path/long-filename.txt
In the example below, !cp:$ searches for the previous command in history that starts with cp and takes the last argument (in this case, which is also the second argument as shown above) of cp and substitutes it for the ls -l command as shown below.
# ls -l !cp:$
ls -l /really/a/very/long/path/long-filename.txt
14. Disable the usage of history using HISTSIZE
If you want to disable history all together and don’t want bash shell to remember the commands you’ve typed, set the HISTSIZE to 0 as shown below.
# export HISTSIZE=0
# history
# [Note that history did not display anything]
15. Ignore specific commands from the history using HISTIGNORE
Sometimes you may not want to clutter your history with basic commands such as pwd and ls. Use HISTIGNORE to specify all the commands that you want to ignore from the history. Please note that adding ls to the HISTIGNORE ignores only ls and not ls -l. So, you have to provide the exact command that you would like to ignore from the history.
# export HISTIGNORE="pwd:ls:ls -ltr:"
# pwd
# ls
# ls -ltr
# service httpd stop
# history | tail -3
79 export HISTIGNORE="pwd:ls:ls -ltr:"
80 service httpd stop
81 history
[Note that history did not record pwd, ls and ls -ltr]
Sed Command in Unix and Linux Examples
Sed is a Stream Editor used for modifying the files in unix (or linux). Whenever you want to make changes to the file automatically, sed comes in handy to do this. Most people never learn its power; they just simply use sed to replace text. You can do many things apart from replacing text with sed. Here I will describe the features of sed with examples.
Consider the below text file as an input.
>cat file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
unixlinux which one you choose.