fgrep Command#

When you need to search for strings that contain many regular expression metacharacters, such as $ and ^, fgrep is very useful. By specifying that the search string contains fixed characters, you don't need to escape each character with a backslash. If the search string contains a newline character, each line will be treated as a single fixed character string to be matched in the search. In other words, fgrep is used to search for fixed characters. Fixed characters mean that the string is interpreted literally - metacharacters do not exist, so regular expressions cannot be used. Running fgrep has the same effect as running grep using the -F option.

Syntax#

fgrep [-b] [-c] [-h] [-i] [-l] [-n] [-s] [-v] [-x] [ -e pattern_list] [-f pattern-file] [pattern] [file]

Parameters#

• -b: Precede each line with the block number it was found in. This is very useful for locating block numbers based on context (the first block is 0).
• -c: Only print the number of lines that contain the pattern.
• -h: Suppress the printing of filenames when searching in multiple files.
• -i: Ignore the case when comparing.
• -l: Print the name of each file once, separated by a newline, that has one or more matching lines. When a pattern appears multiple times, the file name will not be repeated.
• -n: Precede each line within its file with the line number (the first line is 1).
• -s: Work silently, only displaying error messages, which is very useful for checking error status.
• -v: Print only lines that do not contain the pattern.
• -x: Print only lines that match the entire line.
• -e pattern_list: Search for the strings in the pattern list, which is useful when the string starts with -.
• -f pattern-file: Obtain the pattern list from the file.
• pattern: Specify the pattern to be used during the search input.
• file: The pathname of the file to search for patterns. If no file parameter is specified, standard input will be used.

Examples#

The content of the hello.c file is as follows:

#include <stdio.h>
#include <stdlib.h>

int main() {
   printf("Hello World\n");
   printf("Hello World\n");
   printf("Hello World\n");
   return 0;
}

Match lines containing Hello.

fgrep Hello hello.c
#    printf("Hello World\n");
#    printf("Hello World\n");
#    printf("Hello World\n");

Match the number of lines containing Hello.

fgrep -c Hello hello.c
# 3

Reverse the meaning of the match and select lines that do not match Hello.

fgrep -v Hello hello.c
# #include <stdio.h>
# #include <stdlib.h>
#
# int main() {
#    return 0;
# }

Match lines containing i and ignore case.

fgrep -i I hello.c
# #include <stdio.h>
# #include <stdlib.h>
# int main() {
#    printf("Hello World\n");
#    printf("Hello World\n");
#    printf("Hello World\n");

Output only the lines that match the entire line of the file.

fgrep -x "   return 0;" hello.c
#    return 0;

Match lines containing Hello and output the line number.

fgrep -n Hello hello.c
# 5:   printf("Hello World\n");
# 6:   printf("Hello World\n");
# 7:   printf("Hello World\n");

Recursively match files in the current directory that match h*. Please note that because fgrep is used, the command will not interpret * as a wildcard but will treat it as a fixed character *, so there will be no matches. If you use grep with the same parameters, it will output the line numbers and ignore case. Note that the successful matches in the actual terminal will be highlighted in red.

fgrep -rni "h*" ./
# [Empty output]

Daily Question#

References#