Linux Shell / Useful Command Examples
This page provides examples of useful Linux commands. The commands can be run from the command line or used in a shell scripts. See also Useful Script Examples.
Count Matching String in Files
It is often helpful to count instances of a match,
for example how many files contain a string.
This can be used to search code for a pattern that needs attention.
The following uses the grep command to search for a string and count the number of matching files,
for all files in the current folder.
The wc (word count) command is used with -l to count the number of lines.
See the examples of search commands to modify the search.
$ grep 'somestring' * | wc -l
To search for a string, ignoring case and recursively searching all sub-folders:
$ grep -ir 'somestring' | wc -l
To search for a string, ignoring case and recursively searching all sub-folders, and ignoring lines that also contain 'somestring2':
$ grep -ir 'somestring' | grep -v 'somestring2' | wc -l
Find File Differences
The Linux diff command provides a text representation of file differences.
See the diff man page for full usage.
$ diff file1 file2
Compare Files Ignoring Line Endings
Linux uses LF for line endings whereas Windows uses CR LF.
Running diff on files from different operating systems will show every line being different.
To ignore line endings:
$ diff --strip-trailing-cr file1 file2
Search Files for a String
The Linux grep command is useful for searching a file, for example, the following searches for the
pattern by ignoring case (-i) and recursively searching (-r) all files in the current and child folders:
$ grep -ir 'pattern'
$ grep -ir 'error'
The following finds finds including the string error and then filters the
list to files that do not contain help using the -v option.
$ grep -ir 'error' | grep -v 'help'
Search for Files
The Linux find command is used to search for files with name matching a literal string or pattern.
For example, use the following to find log files, searching the current folder (.) and below:
$ find . -name '*.log'
The following is used to find empty folders, which is useful when using Git for version control.
For example, Git may indicate that there are changes but git status does not list any changes.
$ find . -type d -empty
The find command options allow many other choices to match and filter files.