[Linux] Bash fgrep Usage: Search fixed strings in files

Overview

The fgrep command in Bash is used to search for fixed strings in files. Unlike grep, which interprets regular expressions, fgrep treats the search pattern as a literal string, making it useful for searching for specific text without any special character interpretation.

Usage

The basic syntax of the fgrep command is as follows:

fgrep [options] [arguments]

Common Options

• -i: Ignore case distinctions in both the pattern and the input files.
• -v: Invert the match, showing only lines that do not contain the specified string.
• -c: Count the number of lines that match the specified string.
• -l: List the names of files with matching lines, once for each file.
• -n: Prefix each line of output with the line number within its input file.

Common Examples

1. Basic string search in a file:

   fgrep "hello" myfile.txt
   

   This command searches for the string “hello” in myfile.txt.

2. Case-insensitive search:

   fgrep -i "hello" myfile.txt
   

   This command searches for “hello” in a case-insensitive manner.

3. Count occurrences of a string:

   fgrep -c "hello" myfile.txt
   

   This command counts how many lines in myfile.txt contain the string “hello”.

4. List files containing the string:

   fgrep -l "hello" *.txt
   

   This command lists all .txt files in the current directory that contain the string “hello”.

5. Invert match to find lines that do not contain the string:

   fgrep -v "hello" myfile.txt
   

   This command shows all lines in myfile.txt that do not contain the string “hello”.

Tips

• Use fgrep when you need to search for strings that may contain special characters, as it will treat them literally.
• Combine fgrep with other commands using pipes for more complex operations, such as filtering output from other commands.
• Remember that fgrep is often faster than grep when searching for fixed strings, as it does not process regular expressions.