LINUX script bash [duplicate] - linux

Question

I want to check if a file contains a specific string or not in bash. I used this script, but it doesn't work:
if [[ 'grep 'SomeString' $File' ]];then
# Some Actions
fi
What's wrong in my code?

Answer 1

if grep -q SomeString "$File"; then
Some Actions # SomeString was found
fi
You don't need [[ ]] here. Just run the command directly. Add -q option when you don't need the string displayed when it was found.
The grep command returns 0 or 1 in the exit code depending on
the result of search. 0 if something was found; 1 otherwise.
$ echo hello | grep hi ; echo $?
1
$ echo hello | grep he ; echo $?
hello
0
$ echo hello | grep -q he ; echo $?
0
You can specify commands as an condition of if. If the command returns 0 in its exitcode that means that the condition is true; otherwise false.
$ if /bin/true; then echo that is true; fi
that is true
$ if /bin/false; then echo that is true; fi
$
As you can see you run here the programs directly. No additional [] or [[]].

Answer 2

In case if you want to check whether file does not contain a specific string, you can do it as follows.
if ! grep -q SomeString "$File"; then
Some Actions # SomeString was not found
fi

Answer 3

In addition to other answers, which told you how to do what you wanted, I try to explain what was wrong (which is what you wanted.
In Bash, if is to be followed with a command. If the exit code of this command is equal to 0, then the then part is executed, else the else part if any is executed.
You can do that with any command as explained in other answers: if /bin/true; then ...; fi
[[ is an internal bash command dedicated to some tests, like file existence, variable comparisons. Similarly [ is an external command (it is located typically in /usr/bin/[) that performs roughly the same tests but needs ] as a final argument, which is why ] must be padded with a space on the left, which is not the case with ]].
Here you needn't [[ nor [.
Another thing is the way you quote things. In bash, there is only one case where pairs of quotes do nest, it is "$(command "argument")". But in 'grep 'SomeString' $File' you have only one word, because 'grep ' is a quoted unit, which is concatenated with SomeString and then again concatenated with ' $File'. The variable $File is not even replaced with its value because of the use of single quotes. The proper way to do that is grep 'SomeString' "$File".

Answer 4

Shortest (correct) version:
grep -q "something" file; [ $? -eq 0 ] && echo "yes" || echo "no"
can be also written as
grep -q "something" file; test $? -eq 0 && echo "yes" || echo "no"
but you dont need to explicitly test it in this case, so the same with:
grep -q "something" file && echo "yes" || echo "no"

Answer 5

##To check for a particular string in a file
cd PATH_TO_YOUR_DIRECTORY #Changing directory to your working directory
File=YOUR_FILENAME
if grep -q STRING_YOU_ARE_CHECKING_FOR "$File"; ##note the space after the string you are searching for
then
echo "Hooray!!It's available"
else
echo "Oops!!Not available"
fi

Answer 6

grep -q [PATTERN] [FILE] && echo $?
The exit status is 0 (true) if the pattern was found; otherwise blankstring.

Answer 7

if grep -q [string] [filename]
then
[whatever action]
fi
Example
if grep -q 'my cat is in a tree' /tmp/cat.txt
then
mkdir cat
fi

Answer 8

In case you want to checkif the string matches the whole line and if it is a fixed string, You can do it this way
grep -Fxq [String] [filePath]
example
searchString="Hello World"
file="./test.log"
if grep -Fxq "$searchString" $file
then
echo "String found in $file"
else
echo "String not found in $file"
fi
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.)

Answer 9

Try this:
if [[ $(grep "SomeString" $File) ]] ; then
echo "Found"
else
echo "Not Found"
fi

Answer 10

I done this, seems to work fine
if grep $SearchTerm $FileToSearch; then
echo "$SearchTerm found OK"
else
echo "$SearchTerm not found"
fi

Answer 11

grep -q "something" file
[[ !? -eq 0 ]] && echo "yes" || echo "no"