How To Find Files by Content Under UNIX / Linux

1. grep command : print lines matching a pattern.
2. find command : search for files in a directory hierarchy.

Using grep Command To Find Files By Content on Unix or Linux

Type the command as follows:

grep 'string' *.txt
grep 'main(' *.c
grep '#include<example.h>' *.c
grep 'getChar*' *.c
grep -i 'ultra' *.conf
grep -iR 'ultra' *.conf

Where

• -i : Ignore case distinctions in both the PATTERN (match valid, VALID, ValID string) and the input files (math file.c FILE.c FILE.C filename).
• -R (or -r): Read all files under each directory, recursively.

Highlighting searched patterns

You can highlight patterns easily while searching large number of files:
$ grep --color=auto -iR 'getChar();' *.c

Displaying file names and line number for searched patterns

You may also need to display filenames and numbers:
$ grep --color=auto -iRnH 'getChar();' *.c
Where,

• -n : Prefix each line of output with the 1-based line number within its input file.
• -H Print the file name for each match. This is the default when there is more than one file to search.

Hence, type the following command:
$ grep --color=auto -nH 'DIR' *

Fig.01: grep command displaying searched pattern

Using find command to search files by words or string

We can also use the find command. The syntax is as follows:
find /dir/to/search -name "file-pattern" -print | xargs grep "word-to-search"
## OR ##
find /dir/to/search -iname "file-pattern" -print0 | xargs -I {} -0 grep "string-to-search" "{}"
For example, search all c program files (*.c) and look for “main(” and print it on the screen when matched in the current directory:
$ find . -name "*.c" -print | xargs grep "main("
OR
$ find /projects/ -iname "*.c" -print0 | xargs -I {} -0 grep "main(" "{}"
Where find command options are:

• -name : Base of file name. For instance, look for all Perl files (*.pl)
• -iname : Same as above (-name), but the match is case insensitive. For example, the pattern 'prj*' match the file names, Project, project, PROJECT, etc.
• -print : Print the full file name on the standard output.
• -print0 : Display the full file name on the standard output, followed by a null character (instead of the newline character that -print uses). This allows file names that contain newlines or other types of white space to be correctly interpreted by programs that process the find output. This option corresponds to the -0 option of xargs.

And, the xargs command are:

• -I {} : Replace occurrences of {} in the initial-arguments with names read from standard input. In other words, pass {} as input to the grep command.
• -0 : Input items are terminated by a null character instead of by whitespace, and the quotes and backslash are not special (every character is taken literally). Disables the end of file string, which is treated like any other argument. Useful when input items might contain white space, quote marks, or backslashes. The GNU find -print0 option produces input suitable for this mode.
• grep "main(" "{}" : Search for "main(" string using the grep in a file found by find command.

Conclusion

You learned how to find files by content under UNIX and Linux using various commands. See the following resources:

• find command
• grep command
• man pages find and grep