Scripting in Bash

Question

I have a function in bash say parse which takes one argument and function name is f. My file to be processed is somewhat like

a@b@c@
a@d@e@g@
m@n@
t@

I want to give the output as

a@f(b)@f(c)@
a@f(d)@f(e)@f(g)@
m@f(n)@
t@

That is apply function f to all except the first. Any clues so how can I do this?

Keith Thompson · Accepted Answer · 2011-09-27 22:12:44Z

3

This should do it:

sed 's/@\([^@]*\)/@f(\1)/g'

If all the fields are single characters, you can simplify it a bit (say, using . rather than $[^@]*$).

answered Sep 27, 2011 at 22:12

Keith Thompson

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1 Comment

w2lame Over a year ago

For t@ it is giving me t@f() And I have to APPLY the function on the values and not print the statement. That is if the function is square which takes x, then i should print the value of x^2.

Kent · Accepted Answer · 2011-09-28 08:42:57Z

1

maybe this is what you want?

e.g. you have a script called sqr.sh:

kent$  cat sqr.sh
#!/bin/bash
echo $(($1*$1))

now you want to apply the function above on your input:

kent$  echo "foo@2@3@4@
0@10@20@
x@"|awk -F'@' -v OFS=@ '{for(i=2;i<=NF;i++) if($i) "./sqr.sh "$i|getline $i; print}'

foo@4@9@16@
0@100@400@
x@

answered Sep 28, 2011 at 8:42

Kent

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3 Comments

w2lame Over a year ago

this worked like charm except that if there are any spaces in $i then it does some bad things.. i tried combinations like "./sqr.sh $i", "./sqr.sh ${i}", "./sqr.sh ""$i", "./sqr.sh ""${i}" but these didn't work..

Kent Over a year ago

then remove the spaces before you pass it to your script(sqr.sh for example).

w2lame Over a year ago

but there are large number of special characters which I am needed to handle.. anyway thanks a lot :-)

KQ. · Accepted Answer · 2011-09-27 22:12:40Z

1

You could use sed:

sed -e 's/@\(.\)/@f(\1)/g'

answered Sep 27, 2011 at 22:12

KQ.

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6 Comments

w2lame Over a year ago

For t@ it is giving me t@f() And I have to APPLY the function on the values and not print the statement. That is if the function is square which takes x, then i should print the value of x^2.

KQ. Over a year ago

I don't see that result: $ echo "t@" | sed -e 's/@$.$/@f(\1)/g' gives me "t@" as a result.

KQ. Over a year ago

If you need to evaluate the result (and it's valid bash) you can simply enclose it in $(...) to cause the output to be executed.

w2lame Over a year ago

It simply echoes %%%$(parse2(cigar))%%%$(parse2(jump))%%%$(parse2()) rather than applying the function and return the result.

KQ. Over a year ago

It's a little unclear what you're actually trying to accomplish here. Application of bash functions doesn't use parentheses, so I'm not sure that these are bash functions you are trying to call. However, enclosing the entire sed operation with $(...) will cause the output of sed to be executed by bash. HTH.

|

glenn jackman · Accepted Answer · 2011-09-28 00:58:11Z

1

awk 'BEGIN {OFS=FS="@"} {for (i=2; i<=NF-1; i++) $i="f("$i")"; print}'

answered Sep 28, 2011 at 0:58

glenn jackman

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2 Comments

w2lame Over a year ago

query=echo "ab@cd@ef%%%" | awk 'BEGIN {OFS=FS="@"} {for (i=2; i<=NF-1; i++) i=$(func $i); print}' This just hangs on the terminal (or wait for the input though I couldn't really think why). I want to apply function f on the element and not just print it in the output.

glenn jackman Over a year ago

Your question was unclear. Where is the function defined? in awk/shell/...? Note that $() is shell syntax, not bash. For awk, you'd need to use system()

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