How to find lines containing a string in linux

/tmp/myfile

first line text
wanted text
other text

the command

$ grep -n "wanted text" /tmp/myfile | awk -F  ":" '{print $1}'
2

The -n switch to grep prepends any matched line with the line number (followed by :), while the second command uses the colon as a column separator (-F ":") and prints out the first column of any line. The final result is the list of line numbers with a match.

Besides grep, you can also use other utilities such as awk or sed

Here is a few examples. Let say you want to search for a string is in the file named GPL.

Your sample file

user@linux:~$ cat -n GPL 
     1    The GNU General Public License is a free, copyleft license for
     2    The licenses for most software and other practical works are designed
     3  the GNU General Public License is intended to guarantee your freedom to
     4  GNU General Public License for most of our software;
user@linux:~$ 

1. grep

user@linux:~$ grep is GPL 
  The GNU General Public License is a free, copyleft license for
the GNU General Public License is intended to guarantee your freedom to
user@linux:~$ 

2. awk

user@linux:~$ awk /is/ GPL 
  The GNU General Public License is a free, copyleft license for
the GNU General Public License is intended to guarantee your freedom to
user@linux:~$ 

3. sed

user@linux:~$ sed -n '/is/p' GPL
  The GNU General Public License is a free, copyleft license for
the GNU General Public License is intended to guarantee your freedom to
user@linux:~$ 

Hope this helps

The grep family of commands (incl egrep, fgrep) is the usual solution for this.

$ grep pattern filename

If you're searching source code, then ack may be a better bet. It'll search subdirectories automatically and avoid files you'd normally not search (objects, SCM directories etc.)

The usual way to do this is with grep, which uses a regex pattern to match lines:

grep 'pattern' file

Each line which matches the pattern will be output. If you want to search for fixed strings only, use grep -F 'pattern' file. fgrep is shorthand for grep -F.

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You can also use sed:

sed -n '/pattern/p' file

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Or awk:

awk '/pattern/' file