Bash - issue with grep conditional statement
Clash Royale CLAN TAG#URR8PPP
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0
down vote
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Why does this code work correctly, while the other version of the same condition doesn't?
if grep -q string file; then
echo found
else
echo not found
fi
This doesn't work:
if [ ! `grep -q string file` ]; then
echo not found
else
echo found
fi
bash grep test
edited Oct 20 '17 at 9:27
Jeff Schaller
32.1k849109
asked Oct 20 '17 at 8:56
asd
33
add a comment |Â
up vote
0
down vote
favorite
Why does this code work correctly, while the other version of the same condition doesn't?
if grep -q string file; then
echo found
else
echo not found
fi
This doesn't work:
if [ ! `grep -q string file` ]; then
echo not found
else
echo found
fi
bash grep test
edited Oct 20 '17 at 9:27
Jeff Schaller
32.1k849109
asked Oct 20 '17 at 8:56
asd
33
1
Why have you changed the syntax on the two examples?, just a ! to your original example
– Raman Sailopal
Oct 20 '17 at 9:04
Do you know what-qdoes, or are you just blindly using it because you've seen others use it?
– chepner
Oct 21 '17 at 1:27
add a comment |Â
up vote
0
down vote
favorite
up vote
0
down vote
favorite
Why does this code work correctly, while the other version of the same condition doesn't?
if grep -q string file; then
echo found
else
echo not found
fi
This doesn't work:
if [ ! `grep -q string file` ]; then
echo not found
else
echo found
fi
bash grep test
edited Oct 20 '17 at 9:27
Jeff Schaller
32.1k849109
asked Oct 20 '17 at 8:56
asd
33
Why does this code work correctly, while the other version of the same condition doesn't?
if grep -q string file; then
echo found
else
echo not found
fi
This doesn't work:
if [ ! `grep -q string file` ]; then
echo not found
else
echo found
fi
bash grep test
edited Oct 20 '17 at 9:27
Jeff Schaller
32.1k849109
asked Oct 20 '17 at 8:56
asd
33
edited Oct 20 '17 at 9:27
Jeff Schaller
32.1k849109
edited Oct 20 '17 at 9:27
Jeff Schaller
32.1k849109
edited Oct 20 '17 at 9:27
Jeff Schaller
32.1k849109
32.1k849109
asked Oct 20 '17 at 8:56
asd
33
asked Oct 20 '17 at 8:56
asd
33
asked Oct 20 '17 at 8:56
asd
33
33
1
Why have you changed the syntax on the two examples?, just a ! to your original example
– Raman Sailopal
Oct 20 '17 at 9:04
Do you know what-qdoes, or are you just blindly using it because you've seen others use it?
– chepner
Oct 21 '17 at 1:27
add a comment |Â
1
Why have you changed the syntax on the two examples?, just a ! to your original example
– Raman Sailopal
Oct 20 '17 at 9:04
Do you know what-qdoes, or are you just blindly using it because you've seen others use it?
– chepner
Oct 21 '17 at 1:27
1
1
Why have you changed the syntax on the two examples?, just a ! to your original example
– Raman Sailopal
Oct 20 '17 at 9:04
Why have you changed the syntax on the two examples?, just a ! to your original example
– Raman Sailopal
Oct 20 '17 at 9:04
Do you know what
-q does, or are you just blindly using it because you've seen others use it?– chepner
Oct 21 '17 at 1:27
Do you know what
-q does, or are you just blindly using it because you've seen others use it?– chepner
Oct 21 '17 at 1:27
add a comment |Â
1 Answer
1
active
oldest
votes
up vote
5
down vote
accepted
`grep -q string file`, in backticks (or inside $(...), which is preferable), will be replaced by the output of grep. This will be an empty string since -q is used.
To negate a test, just insert ! before it:
if ! grep -q pattern file; then
echo not found
else
echo found
fi
If you truly want to search for a string (rather than a regular expression), then you should use -F with grep as well.
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
5
down vote
accepted
`grep -q string file`, in backticks (or inside $(...), which is preferable), will be replaced by the output of grep. This will be an empty string since -q is used.
To negate a test, just insert ! before it:
if ! grep -q pattern file; then
echo not found
else
echo found
fi
If you truly want to search for a string (rather than a regular expression), then you should use -F with grep as well.
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
add a comment |Â
up vote
5
down vote
accepted
`grep -q string file`, in backticks (or inside $(...), which is preferable), will be replaced by the output of grep. This will be an empty string since -q is used.
To negate a test, just insert ! before it:
if ! grep -q pattern file; then
echo not found
else
echo found
fi
If you truly want to search for a string (rather than a regular expression), then you should use -F with grep as well.
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
add a comment |Â
up vote
5
down vote
accepted
up vote
5
down vote
accepted
`grep -q string file`, in backticks (or inside $(...), which is preferable), will be replaced by the output of grep. This will be an empty string since -q is used.
To negate a test, just insert ! before it:
if ! grep -q pattern file; then
echo not found
else
echo found
fi
If you truly want to search for a string (rather than a regular expression), then you should use -F with grep as well.
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
`grep -q string file`, in backticks (or inside $(...), which is preferable), will be replaced by the output of grep. This will be an empty string since -q is used.
To negate a test, just insert ! before it:
if ! grep -q pattern file; then
echo not found
else
echo found
fi
If you truly want to search for a string (rather than a regular expression), then you should use -F with grep as well.
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
edited Oct 20 '17 at 11:07
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
answered Oct 20 '17 at 9:19
Kusalananda
105k14209326
105k14209326
add a comment |Â
add a comment |Â
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1
Why have you changed the syntax on the two examples?, just a ! to your original example
– Raman Sailopal
Oct 20 '17 at 9:04
Do you know what
-qdoes, or are you just blindly using it because you've seen others use it?– chepner
Oct 21 '17 at 1:27