10 Easy Examples of GNU sed Command Lines Episode 3

10 Easy Examples of GNU sed Command Lines Episode 3

Previously, we provided the first and second articles about GNU sed command line examples. Now it is the third article covering combination between sed and bash to do daily life jobs. We begin to focus in daily life jobs in this episode. This episode is a continuation of our previous articles. So if you miss something here, we suggest you to read the two previous episodes.

Text Examples

text6.txt:

gnu gnu gnu gnu unix

bsd bsd bsd bsd unix

unix unix unix unix

minix minix minix unix

As previous articles go, save this file in your /tmp and perform all sed commands there. 

21. Run Multiple Commands

Command Example:

sed -e s/gnu/U&/g -e s/bsd/U&/g text6.txt

Output Example:

master@master:/tmp$ sed -e s/gnu/U&/g -e s/bsd/U&/g text6.txt

GNU GNU GNU GNU unix

BSD BSD BSD BSD unix

unix unix unix unix

minix minix minix unix

master@master:/tmp$

Explanation:

We see the only different here compared to our previous examples, is, the `-e` option. This option handles one command or script of sed, so putting two of this options means doing two sed commands simultaneously. You may put more `-e` option to do more commands. See, in this example there are two `s///g` command sequences. See the result, there are two lines result (uppercased strings) from the two commands. 

22. Run Multiple Commands (Simpler)

Command Example:

sed s/gnu/U&/g; s/bsd/U&/g text6.txt

Output Example:

master@master:/tmp$ sed s/gnu/U&/g; s/bsd/U&/g text6.txt

GNU GNU GNU GNU unix

BSD BSD BSD BSD unix

unix unix unix unix

minix minix minix unix

master@master:/tmp$

Explanation: 

This example is simpler compared the number 21 example. It has the same result, but without the `-e` option. Instead, this commands make use of (`;`) character to separate two commands inside a pair of single quotes (`� �`). 

23. Combine sed with bash Looping Commands

Command Examples:

for i in {6..8}; do sed /bsd/d "text$i.txt"; echo ""; done;

Output Examples:

(1)

master@master:/tmp$ for i in {6..8}; do sed /bsd/d "text$i.txt"; echo ""; done;

gnu gnu gnu gnu unix

unix unix unix unix

minix minix minix unix

vms vms vms

unix dunix ultrix irix tru64

hp-ux sunos solaris

xnu hurd linux

(2)

master@master:/tmp$ for i in {6..8}; do sed /bsd/!d "text$i.txt"; echo ""; done;

bsd bsd bsd bsd unix

unix bsd unix unix

gnu gnu gnu bsd

minix minix minix minix bsd

bsd darwin

master@master:/tmp$

Explanation:

This is the first time within all episodes we use combination of GNU sed and GNU bash. Here, we make use of bash `for` command for looping. For the first timer, those two examples above perhaps makes no sense. But if you look one command in a programming manner you will understand it easier. For example, the first command above can be written like this:

for i in {6..8};

do

sed /bsd/d "text$i.txt";

echo "";

done;

This code is GNU bash scripting language. To read it properly, we can analyze it one by one:

1. The first line sets a variable named `i` to contain numbers from 6 until 8 (hence, there would be 3 loops). Every loop will have `i` to contain one number, so the first loop i = 6, second loop i = 7, and third loop i = 8.
2. The second line is a starting point of loop, to wrap the actual command line to do the actual job.
3. The third line is the actual code. This is your sed command to do deleting any line containing �bsd� string. This is the actual job.
4. The fourth line is also the command line to do the job, like the sed line, but it is just secondary. The most important command is still the third line. This fourth line does the job to give newlines so the final output will be easier to read.
5. The fifth line is an ending point of loop, pairing with the second line (so there are do and done).
6. Conclusion: this code means do the sed command line, but do loop it 3 times, for the number 6 until number 8, towards the file text6.txt then text7.txt then text8.txt. The `i` variable does the job for substituting number in every file name.
7. These five lines can be written in a single line like the first command example here. 
    

24. Delete Contents of Multiple Files� (bash Looping)

Command Example:

for i in {6..8}; do sed -i d text$i.txt; done

Output Examples:

master@master:/tmp$ for i in {6..8}; do sed -i d text$i.txt; done

master@master:/tmp$ for i in {6..8}; do cat text$i.txt; done

master@master:/tmp$

Explanation:

This example is just the same with the example number 23. It is also a bash looping code in single line. This code means do the sed command line, but do loop it three times, for the number 6 until 8, towards the file text6.txt, text7.txt, text8.txt. The sed command is just �d�, it means delete the whole content of file. So this single line command do erase all the contents of text6.txt, text7.txt, text8.txt. 

WARNING: this sed `-i` option and d command result in deleting contents of the files. Be careful, make sure you dont delete important contents.

25. Rename Multiple Files (bash Looping)

Command Examples:

1. for i in *.txt; do mv "$i" "`echo $i | sed "s/text/flext/g"`"; done
2. for i in *.txt; do mv -v "$i" "`echo $i | sed "s/^[0-9]*[0-9]//g"`"; done

Output Examples:

(1)

master@master:/tmp$ ls

text6.txt

text7.txt

text8.txt

master@master:/tmp$ for i in *.txt; do mv "$i" "`echo $i | sed "s/text/flext/g"`"; done

master@master:/tmp$ ls

flext6.txt

flext7.txt

flext8.txt

master@master:/tmp$

(2)

master@master:/tmp$ touch 1lion.txt 2tiger.txt 3giraffe.txt 4monkey.txt 5eagle.txt 6deer.txt

master@master:/tmp$ ls

1lion.txt

2tiger.txt

3giraffe.txt

4monkey.txt

5eagle.txt

6deer.txt

master@master:/tmp$ for i in *.txt; do mv -v "$i" "`echo $i | sed "s/^[0-9]*[0-9]//g"`"; done

1lion.txt -> lion.txt

2tiger.txt -> tiger.txt

3giraffe.txt -> giraffe.txt

4monkey.txt -> monkey.txt

5eagle.txt -> eagle.txt

6deer.txt -> deer.txt

mv: flext.txt and flext.txt are the same file

master@master:/tmp$

Explanation:

First example do the rename loops towards some .txt files with number in every beginning of their file names.

• The loop is basically mv command, but the argument of this mv is handled by echo and sed.
• The echo command print the $i. This $i is a notation of the `i` variable content. Command echo print this in every loop.
• The sed command receive the echo output via the `|` (pipe). So sed processes it, find and replace the �text� string into �flext� string.
• This loop repeated until the filename text6.txt become flext6.txt, so on until text8.txt become flext8.txt.
• You should pay attention to the usage or quotation marks (� �) and the apostrophe marks (` `). Place them properly just like the example. 
  
  
   

26. Delete Multiple Files (bash Looping)

Command Examples:

1. for i in *.txt; do rm -v "`echo $i | sed "s/^[0-9]*[0-9]//g"`"; done
2. for i in *.txt; do rm -v "`echo $i | sed -n "/^[0-9]*[0-9]/p"`"; done

Output Examples:

(1)

master@master:/tmp$ ls -w 1 *.txt

1lion.txt

2tiger.txt

3giraffe.txt

4monkey.txt

5eagle.txt

6deer.txt

deer.txt

eagle.txt

flext.txt

giraffe.txt

lion.txt

monkey.txt

tiger.txt

master@master:/tmp$ for i in *.txt; do rm -v "`echo $i | sed "s/^[0-9]*[0-9]//g"`"; done

removed lion.txt

removed tiger.txt

removed giraffe.txt

removed monkey.txt

removed eagle.txt

removed deer.txt

master@master:/tmp$ ls

1lion.txt

2tiger.txt

3giraffe.txt

4monkey.txt

5eagle.txt

6deer.txt

(2)

master@master:/tmp$ ls -w 1 *.txt

1lion.txt

2tiger.txt

3giraffe.txt

4monkey.txt

5eagle.txt

6deer.txt

elephant2.txt

giraffe4.txt

lion1.txt

monkey3.txt

tiger5.txt

master@master:/tmp$ for i in *.txt; do rm -v "`echo $i | sed -n "/^[0-9]*[0-9]/p"`"; done

removed 1lion.txt

removed 2tiger.txt

removed 3giraffe.txt

removed 4monkey.txt

removed 5eagle.txt

removed 6deer.txt

master@master:/tmp$ ls -w 1 *.txt

elephant2.txt

giraffe4.txt

lion1.txt

monkey3.txt

tiger5.txt

master@master:/tmp$

Explanation:

This example number 26 basically the same with number 25 except mv being rm. Here, we try to delete beginning-numbered file names and non-beginning numbered file names. We use substitution at the first example, and deletion at the second example. 

WARNING: this rm command is already dangerous, combined with bash looping commands it would be extremely dangerous. Be careful, make sure you dont make any regex or syntax mistake. Please avoid using sudo if you dont know what will happen.

27. Change Slash Delimiters to Another Characters

Command Examples:

1. sed s/unix/CHANGED/g text6.txt
2. sed s@unix@CHANGED@g text6.txt
3. sed s!unix!CHANGED!g text6.txt
4. sed s?unix?CHANGED?g text6.txt

Output Examples:

master@master:/tmp$ sed s/unix/CHANGED/g text6.txt

gnu gnu gnu gnu CHANGED

bsd bsd bsd bsd CHANGED

CHANGED CHANGED CHANGED CHANGED

minix minix minix CHANGED

master@master:/tmp$ sed s@unix@CHANGED@g text6.txt

gnu gnu gnu gnu CHANGED

bsd bsd bsd bsd CHANGED

CHANGED CHANGED CHANGED CHANGED

minix minix minix CHANGED

master@master:/tmp$ sed s!unix!CHANGED!g text6.txt

gnu gnu gnu gnu CHANGED

bsd bsd bsd bsd CHANGED

CHANGED CHANGED CHANGED CHANGED

minix minix minix CHANGED

master@master:/tmp$ sed s?unix?CHANGED?g text6.txt

gnu gnu gnu gnu CHANGED

bsd bsd bsd bsd CHANGED

CHANGED CHANGED CHANGED CHANGED

minix minix minix CHANGED

master@master:/tmp$

Explanation:

Using slash for sed command regex delimiters is sometimes confusing. Especially, if your regex contains many slashes too. The solution is you must use delimiters other than slash. As long as they are used consistently, you may use characters like at, exclamation mark, question mark, or underscore to replace the slash. The examples shown in this number 27 have the same commands and the same results. The only difference is the delimiter (`@`, `!`, and `?`). 

28. Adjust Line Spacing (Single)

Command Examples:

Output Examples:

master@master:/tmp$ cat text6.txt

gnu gnu gnu gnu unix

bsd bsd bsd bsd unix

unix unix unix unix

minix minix minix unix

master@master:/tmp$ sed �G� text6.txt

gnu gnu gnu gnu unix

bsd bsd bsd bsd unix

unix unix unix unix

minix minix minix unix

Explanation:

This single �G� command of sed causes addition one blank line for every line. 

29. Adjust Line Spacing (Double)

Command Example:

Output Example:

master@master:/tmp$ sed G;G text6.txt

gnu gnu gnu gnu unix

bsd bsd bsd bsd unix

unix unix unix unix

minix minix minix unix

master@master:/tmp$

Explanation:

This double `G` command (separated with a (`;`) character) gives every line addition of two blank lines. 

30. Find & Replace (Lines Range)

Command Examples:

Output Examples:

master@master:/tmp$ sed 1,3 s/unix/CHANGED/g text6.txt

gnu gnu gnu gnu CHANGED

bsd bsd bsd bsd CHANGED

CHANGED CHANGED CHANGED CHANGED

minix minix minix unix

master@master:/tmp$

Explanation:

You may determine the range of lines for sed command, not only �the coordinate�. See the two numbers separated with comma (`,`) above. That command means do substitution command only for line number 1 until line number 3.