How to test if string exists in file with Bash?
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 asgrep
,cmp
, anddiff
, 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.