Shell Script: Truncating String

Question

I have two folders full of trainings and corresponding testfiles and I'd like to run the fitting pairs against each other using a shell script.

This is what I have so far:

for x in SpanishLS.train/*.train
do
    timbl -f $x -t SpanishLS.test/$x.test
done

This is supposed to take file1(-n).train in one directory, look for file1(-n).test in the other, and run them trough a tool called timbl. What it does instead is look for a file called SpanishLS.train/file1(-n).train.test which of course doesn't exist. What I tried to do, to no avail, is truncate $x in a way that lets the script find the correct file, but whenever I do this, $x is truncated way too early, resulting in the script not even finding the .train file.

How should I code this?

Jonathan Leffler · Accepted Answer · 2012-08-12 18:13:49Z

4

If I got you right, this will do the job:

for x in SpanishLS.train/*.train
do
    y=${x##*/}  # strip basepath
    y=${y%.*} # strip extention
    timbl -f $x -t SpanishLS.test/$y.test
done

edited Aug 12, 2012 at 18:13

Jonathan Leffler

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answered Aug 12, 2012 at 17:38

Alan

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Comments

Jonathan Leffler · Accepted Answer · 2012-08-12 18:12:09Z

2

Use basename:

for x in SpanishLS.train/*.train
do
    timbl -f $x -t SpanishLS.test/$(basename "$x" .train).test
done

That removes the directory prefix and the .train suffix from $x, and builds up the name you want.

In bash (and other POSIX-compliant shells), you can do the basename operation with two shell parameter expansions without invoking an external program. (I don't think there's a way to combine the two expansions into one.)

for x in SpanishLS.train/*.train
do
    y=${x##*/}                                        # Remove path prefix
    timbl -f $x -t SpanishLS.test/${y%.train}.test    # Remove .train suffix
done

Beware: bash supports quite a number of (useful) expansions that are not defined by POSIX. For example, ${y//.train/.test} is a bash-only notation (or bash and compatible shells notation).

edited Aug 12, 2012 at 18:12

answered Aug 12, 2012 at 17:33

Jonathan Leffler

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3 Comments

tripleee Over a year ago

The substitutions are not Bash only, but POSIX sh, aren't they?

Jonathan Leffler Over a year ago

@tripleee Hmmm...yes, the ## and % (and # and %%) expansions are in POSIX shell. Another comment elsewhere suggests ${x//.train/.test}; that is not a POSIX expansion. I've updated my answer—thanks for pointing this out.

lhausmann Over a year ago

Thanks! That was way more elegant than I imagined!

Igor Chubin · Accepted Answer · 2012-08-12 17:34:58Z

0

Replace all occurences of .train in the filename to .text:

timbl -f $x -t $(echo $x | sed 's/\.train/.text/g')

answered Aug 12, 2012 at 17:34

Igor Chubin

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2 Comments

glenn jackman Over a year ago

can do this just in bash: -t ${x//.train/.test}

Jonathan Leffler Over a year ago

This does not deal with the SpanishLS.train vs SpanishLS.test path prefixes.

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