Given a plain text file containing
FOO=foo
BAR=bar
BAZ=baz
How do we grep for the value using the key?
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A dirty alternative: If the file looks like what your have pasted, source the file and use $BAR, $BAZ directly. PS: Dont follow this suggestion, you'll instantly encounter many corner cases. – UltraInstinct Jun 11 '15 at 09:21
4 Answers
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Use a look behind:
$ grep -Po '(?<=^FOO=)\w*$' file
foo
I also like awk for it:
$ awk -v FS="FOO=" 'NF>1{print $2}' file
foo
Or even better:
$ awk -F= -v key="FOO" '$1==key {print $2}' file
foo
With sed:
$ sed -n 's/^FOO=//p' file
foo
Or even with Bash -ONLY if you are confident about the file not containing any weird values-, you can source the file and echo the required value:
$ (source file; echo "$FOO")
foo
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these are quite common tools with common approaches. If anybody needs some explanation, just ping me and I will add them! – fedorqui Jun 11 '15 at 09:58
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how to grep a value from FOO in entire path instead of giving a particular file? – Nandhakumar Kittusamy Mar 08 '19 at 11:53
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@NandhaKumar you may want to check [How do I find all files containing specific text on Linux?](https://stackoverflow.com/q/16956810/1983854) – fedorqui Mar 09 '19 at 14:54
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Careful with `awk -v FS="FOO="` because it will return the value for any keys with partial matches; e.g.: `echo -en 'AFOO=oops\nFOO=bar' | awk -v FS='FOO=' 'NF>1{print $2}'` returns both `oops` and `bar`. Use `FS='^FOO='` to get the exact match. – Thiago Figueiro Jun 10 '19 at 01:59
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Simple way:
grep "^FOO=" | cut -d"=" -f2-
I prefer this because it's very easy to remember for me.
Explanation: It simply greps the line starting with FOO (hence the ^) and cutting it with = to pieces and then getting the second piece with -f2-.
Inanc Gumus
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2Beware that this won't return the correct value if the value has `=` in it. E.g.: `echo 'FOO=bar=oops' | grep "^FOO=" | cut -d"=" -f2` incorrectly returns `bar`. Using `f-2-` returns the correct value `bar=oops` – Thiago Figueiro Jun 10 '19 at 01:54
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This is the perfect answer if you make little modification like what @ThiagoFigueiro told. (it has been 4 years). – MaXi32 Jan 09 '21 at 23:26
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I tried to update the answer 4 years ago but SO doesn't allow 1-character changes so ♂️ – Thiago Figueiro Jan 22 '21 at 07:02
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Using `f-2-`, as suggested in a comment above, seems to be wrong. Using `-f2-` works for me. – payne Dec 02 '21 at 01:36
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Try this one too...
grep "^FOO=" file.txt | awk -F"=" '{ print $2 }'
With some help from @fedorqui
CrazyMenConnected
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`grep` + `awk` normally means that `awk` alone can handle it. Also, what if we have a line `hello=FOO`? This would return `FOO`, whereas `hello` is not the given key. – fedorqui Jun 11 '15 at 09:24
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To make it works always, use `^FOO=`. This way, it will match the beginning of the line. – fedorqui Jun 11 '15 at 09:37
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1Ah thanks, I didn’t knew that! I was trying to help someone with a doubt, and I was the one that ended up learning something! Thanks @fedorqui! – CrazyMenConnected Jun 11 '15 at 09:40
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This won't work when you have value like this (as seen in complex password): `echo 'FOO==FO=bar=oo==ps=pk' | grep "^FOO=" | awk -F"=" '{ print $2 }'`, it returns nothing. it should return `=FO=bar=oo==ps=pk`. I think the best answer when using grep is from @Inanc Gumus with little modification from @Thiago's comment – MaXi32 Jan 09 '21 at 23:20
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Another proposition : split the work
grep "FOO=" file.txt | sed -e 's/.*=//'
grep will fetch the correct lines
sed will remove anything up to the (last) equal sign
Bruce
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Try this and you will be disappointed with this answer: `echo 'FOO==FO=bar=oo==ps=pk' | grep "FOO=" | sed -e 's/.*=//'` This should return `=FO=bar=oo==ps=pk` but it returns only `pk` – MaXi32 Jan 09 '21 at 23:28