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About string : How-to-test-if-string-exists-in-file-with-Bash

Question Detail

I have a file that contains directory names:

my_list.txt :

/tmp
/var/tmp

I’d like to check in Bash before I’ll add a directory name if that name already exists in the file.

Question Answer

grep -Fxq “$FILENAME” my_list.txt

The exit status is 0 (true) if the name was found, 1 (false) if not, so:
if grep -Fxq “$FILENAME” my_list.txt
then
# code if found
else
# code if not found
fi

Explanation
Here are the relevant sections of the man page for grep:

grep [options] PATTERN [FILE…]

-F, –fixed-strings
        Interpret PATTERN as a list of fixed strings, separated by newlines, any of which is to be matched.
-x, –line-regexp
        Select only those matches that exactly match the whole line.
-q, –quiet, –silent
        Quiet; do not write anything to standard output. Exit immediately with zero status if any match is found, even if an error was detected. Also see the -s or –no-messages option.

Error handling
As rightfully pointed out in the comments, the above approach silently treats error cases as if the string was found. If you want to handle errors in a different way, you’ll have to omit the -q option, and detect errors based on the exit status:

Normally, the exit status is 0 if selected lines are found and 1 otherwise. But the exit status is 2 if an error occurred, unless the -q or –quiet or –silent option is used and a selected line is found. Note, however, that POSIX only mandates, for programs such as grep, cmp, and diff, that the exit status in case of error be greater than 1; it is therefore advisable, for the sake of portability, to use logic that tests for this general condition instead of strict equality with 2.

To suppress the normal output from grep, you can redirect it to /dev/null. Note that standard error remains undirected, so any error messages that grep might print will end up on the console as you’d probably want.
To handle the three cases, we can use a case statement:
case `grep -Fx “$FILENAME” “$LIST” >/dev/null; echo $?` in
0)
# code if found
;;
1)
# code if not found
;;
*)
# code if an error occurred
;;
esac

……………………………………………………
Regarding the following solution:

grep -Fxq “$FILENAME” my_list.txt

In case you are wondering (as I did) what -Fxq means in plain English:

F: Affects how PATTERN is interpreted (fixed string instead of a regex)
x: Match whole line
q: Shhhhh… minimal printing

From the man file:

-F, –fixed-strings
Interpret PATTERN as a list of fixed strings, separated by newlines, any of which is to be matched.
(-F is specified by POSIX.)
-x, –line-regexp
Select only those matches that exactly match the whole line. (-x is specified by POSIX.)
-q, –quiet, –silent
Quiet; do not write anything to standard output. Exit immediately with zero status if any match is
found, even if an error was detected. Also see the -s or –no-messages option. (-q is specified by
POSIX.)

……………………………………………………
Three methods in my mind:

1) Short test for a name in a path (I’m not sure this might be your case)

ls -a “path” | grep “name”

2) Short test for a string in a file

grep -R “string” “filepath”

3) Longer bash script using regex:

#!/bin/bash

declare file=”content.txt”
declare regex=”\s+string\s+”

declare file_content=$( cat “${file}” )
if [[ ” $file_content ” =~ $regex ]] # please note the space before and after the file content
then
echo “found”
else
echo “not found”
fi

exit

This should be quicker if you have to test multiple string on a file content using a loop for example changing the regex at any cicle.
……………………………………………………
Easiest and simplest way would be:

isInFile=$(cat file.txt | grep -c “string”)

if [ $isInFile -eq 0 ]; then
#string not contained in file
else
#string is in file at least once
fi

grep -c will return the count of how many times the string occurs in the file.
……………………………………………………
Simpler way:

if grep “$filename” my_list.txt > /dev/null
then
… found
else
… not found
fi

Tip: send to /dev/null if you want command’s exit status, but not outputs.
……………………………………………………
If I understood your question correctly, this should do what you need.

you can specifiy the directory you would like to add through $check variable
if the directory is already in the list, the output is “dir already listed”
if the directory is not yet in the list, it is appended to my_list.txt

In one line: check=”/tmp/newdirectory”; [[ -n $(grep “^$check\$” my_list.txt) ]] && echo “dir already listed” || echo “$check” >> my_list.txt
……………………………………………………
grep -E “(string)” /path/to/file || echo “no match found”

-E option makes grep use regular expressions
……………………………………………………
Here’s a fast way to search and evaluate a string or partial string:
if grep -R “my-search-string” /my/file.ext
then
# string exists
else
# string not found
fi

You can also test first, if the command returns any results by running only:
grep -R “my-search-string” /my/file.ext

……………………………………………………
The @Thomas’s solution didn’t work for me for some reason but I had longer string with special characters and whitespaces so I just changed the parameters like this:

if grep -Fxq ‘string you want to find’ “/path/to/file”; then
echo “Found”
else
echo “Not found”
fi

Hope it helps someone
……………………………………………………
If you just want to check the existence of one line, you do not need to create a file. E.g.,

if grep -xq “LINE_TO_BE_MATCHED” FILE_TO_LOOK_IN ; then
# code for if it exists
else
# code for if it does not exist
fi

……………………………………………………
My version using fgrep

FOUND=`fgrep -c “FOUND” $VALIDATION_FILE`
if [ $FOUND -eq 0 ]; then
echo “Not able to find”
else
echo “able to find”
fi

……………………………………………………
I was looking for a way to do this in the terminal and filter lines in the normal “grep behaviour”. Have your strings in a file strings.txt:
string1
string2

Then you can build a regular expression like (string1|string2|…) and use it for filtering:
cmd1 | grep -P “($(cat strings.txt | tr ‘\n’ ‘|’ | head -c -1))” | cmd2

Edit: Above only works if you don’t use any regex characters, if escaping is required, it could be done like:
cat strings.txt | python3 -c “import re, sys; [sys.stdout.write(re.escape(line[:-1]) + ‘\n’) for line in sys.stdin]” | …

……………………………………………………
A grep-less solution, works for me:

MY_LIST=$( cat /path/to/my_list.txt )

if [[ “${MY_LIST}” == *”${NEW_DIRECTORY_NAME}”* ]]; then
echo “It’s there!”
else
echo “its not there”
fi

based on:
https://stackoverflow.com/a/229606/3306354
……………………………………………………
grep -Fxq “String to be found” | ls -a

grep will helps you to check content
ls will list all the Files

……………………………………………………
Slightly similar to other answers but does not fork cat and entries can contain spaces
contains() {
[[ ” ${list[@]} ” =~ ” ${1} ” ]] && echo ‘contains’ || echo ‘does not contain’
}

IFS=$’\r\n’ list=($(

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