How To Find Files by Content Under UNIX

I had written lots of code in C for my school work and saved it as source code under /home/user/c/*.c and *.h. How do I find files by content such as string or words (function name such as main() under UNIX shell prompt?

You need to use the following tools:
[a] grep command : print lines matching a pattern.
[b] find command: search for files in a directory hierarchy.

grep Command To Find Files By Content

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 : 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.

$grep --color=auto -nH 'DIR' *
Sample output:

Fig.01: grep command displaying searched pattern

You can also use find command:
$ find . -name "*.c" -print | xargs grep "main("