Shell Script - Using the diff command

Question

This doesn't seem to be working correctly.
$4 is a C file. $in is the input file. $5 is a newly created output file, after $in inputs to $4 (I'm not really sure about this one.)

$out is an output that I created before running the script.

After, I'm comparing $5 and $out to see if they are equal.

I'm just wondering what does the ; mean.

    $4 < $in > $5
    if  diff $5 $out  >/dev/null 2>&1 ;  
    then
       echo "same!"
    else
       echo "different!"
    fi

(This is in Bourne Shell)

Seriously? All that and what you're asking is what ; does in sh? — melpomene
– melpomene, Commented Nov 27, 2012 at 4:00
I'm also asking about the $5 part. lol. I'll try to make that into a question. — Jonathan Lam
– Jonathan Lam, Commented Nov 27, 2012 at 4:03
lol ok. How do I compare the output of $4 < $in" to $out ? (I don't think I need $5.) — Jonathan Lam
– Jonathan Lam, Commented Nov 27, 2012 at 4:08
Will we regret it if we ask what $1, $2 and $3 represent? What exactly are you trying to do? Please explain at a high level. (For example, "I'm trying to compare the old and new versions of a C source file after compiling them to ensure they're both sound", except that only seems to require two arguments and not $in or $out too.) — Jonathan Leffler
– Jonathan Leffler, Commented Nov 27, 2012 at 4:14

Jonathan Leffler · Accepted Answer · 2012-11-27 05:35:42Z

1

The semi-colon is redundant, but marks the end of the diff command. It could have been followed by another command, but isn't.

[I've removed some comments based on a misunderstanding of what a 'C file' is. In this context, it means a 'program written in C' rather than a C source file.]

edited Nov 27, 2012 at 5:35

answered Nov 27, 2012 at 4:04

Jonathan Leffler

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2 Comments

Jonathan Lam Over a year ago

oh sorry, about the confusion.

Jonathan Lam Over a year ago

I think I found my problem.

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