AWK How to replace a field using 2 shell variables?

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07-28-2011

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AWK How to replace a field using 2 shell variables?

Hello everybody:
I want to replace any field $2 of any file line (f.i. test.txt) matching $1 with a shell variable.

Code:

$ cat test.txt    
F       0
B       A
H       -12.33

Now I'm going to ask the value of variable B:

Code:

$ SEARCHVAR=B
$ OLDVAL=$(awk -v SEARCHVAR="$SEARCHVAR" '$1==SEARCHVAR {print $2}' test.txt)
$ echo $OLDVAL
A

And finally i tries to replace this value ("A") from field 2 by another shell variable with "10", using awk again:

Code:

$ NEWVAL=10
$ awk -v SEARCHVAR="$SEARCHVAR" OLDVAL="$OLDVAL" NEWVAL="$NEWVAL" '{if($1==SEARCHVAR && $2==OLDVAL) sub{OLDVAL,NEWVAL,$2} {print}}' test.txt

Unfortunately I only gets fatal error messages again & again.
Can you help me, please?
Thanks all in advace.

Last edited by basalt; 07-28-2011 at 04:42 PM..

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Code:

# cat file
F 0
B A
H -12.33
# awk -vSEARCHVAR="B" -vOLDVAL="A" -vNEWVAL=10 '$1==SEARCHVAR && $2==OLDVAL{sub(OLDVAL,NEWVAL,$2)}1' file
F 0
B 10
H -12.33

PS: Please use [code] tags when you post code or data sample.

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I just edited it with codes danmero.

Your solution was not able for me. I can't to look the old value from a file every time i needs to change it. I must that the shell do it by itself. But thanks to it, finally I found with the solution:

Code:

#!/bin/bash
SEARCHVAR=B
NEWVAL=10
OLDVAL=$(awk -v SEARCHVAR="$SEARCHVAR" '$1==SEARCHVAR {print $2}' test.txt)
awk -vSEARCHVAR="$SEARCHVAR" -vOLDVAL="$OLDVAL" -vNEWVAL="$NEWVAL" '$1==SEARCHVAR && $2==OLDVAL{sub(OLDVAL,NEWVAL,$2)}1' test.txt

the shell will show this:

Code:

A       0
B 10
C       -12.33

I hope this can to help it to someone

Last edited by basalt; 07-28-2011 at 06:23 PM..

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07-28-2011

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Code:

# cat file
F       0
B       A
H       -12.33
# SEARCHVAR=B
# NEWVAL=10
# awk -vSEARCHVAR="$SEARCHVAR" -vNEWVAL="$NEWVAL" '$1==SEARCHVAR{$2=NEWVAL}1' OFS=\\t file
F       0
B       10
H       -12.33

If that's what you want , you don't need to parse the file twice.

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07-29-2011

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Quote:

Originally Posted by danmero

Code:

# cat file
F       0
B       A
H       -12.33
# SEARCHVAR=B
# NEWVAL=10
# awk -vSEARCHVAR="$SEARCHVAR" -vNEWVAL="$NEWVAL" '$1==SEARCHVAR{$2=NEWVAL}1' OFS=\\t file
F       0
B       10
H       -12.33

If that's what you want , you don't need to parse the file twice.

Oh yes!! That is an awsome solution. Thanks a lot !

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