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I have a binary file with a trailing CRLF (2 bytes total) that I want to remove. How should I do it? Please note that I'm using busybox and I don't have perl.

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2  
Is it trailing each line, or only the end of the file? –  bahamat Aug 29 '12 at 15:51
    
Only at the end of file. Any other CRLF should be ignored. –  michelemarcon Aug 30 '12 at 7:26

3 Answers 3

up vote 3 down vote accepted

With a typical BusyBox installation, I think you're going to have to parse the output of ls to get the size. Once you have the size, extract the first n-2 bytes of the file with head.

size=$(ls -l -- "$file" | awk 'NR==1 {print $5}')
head -c $(($size - 2)) <"$file" >"$file.new"

If you want to truncate the file in place, use dd.

size=$(ls -l -- "$file" | awk 'NR==1 {print $5}')
dd if=/dev/null of="$file" bs=$(($size - 2)) seek=1
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Rather than parsing ls, busybox often has stat features compiled in. If that's the case here, use size=$(busybox stat -c '%s' "$file") or just size=$(stat -c '%s' "$file") instead. –  cas Aug 30 '12 at 2:34
    
Wouldn't wc -c < "$file" be an easier and safer way to get the file size than parsing ls? Or is wc often left out of busybox? –  jw013 Aug 30 '12 at 2:34
    
@CraigSanders stat is good if it's included, but it isn't always included. I chose commands with a high likelihood of being included. For example, my router doesn't have stat. –  Gilles Aug 30 '12 at 2:42
    
@jw013 wc in BusyBox reads the whole file and counts the bytes (unlike GNU coreutils and IIRC *BSD, which optimize wc <foo and wc foo to read the file size with stat(2)). –  Gilles Aug 30 '12 at 2:43
    
@Gilles Ah, makes sense, thanks. –  jw013 Aug 30 '12 at 2:48

Get the size of the file, substract two. You obtain $n and run

dd bs=1 seek=$n < /dev/null of=the-file

Or if you have truncate

truncate  -s -2 the-file
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He's using busybox so truncate is probably not there. But dd probably is, and I like that solution if there's only one line in the file, or the CFLF is only at the end of the file. –  bahamat Aug 29 '12 at 15:53
tr -d '\013' < input > output
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3  
This would delete all vertical tabs in the file, not a trailing CRLF –  Michael Mrozek Aug 30 '12 at 3:24

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