Command line question

igotlongestname has asked for the wisdom of the Perl Monks concerning the following question:

I have a program written a while ago, with a Perl command line call, which I am having trouble deciphering. I think it may be using some older Perl syntax that I'm not familiar with (or possibly I am just not reading the line right). Here is the command:

perl -ni -e's+${SOURCE}/${SAMS}/++g;s+${SOURCE}/${SAMLIB}/++g;s+${SOUR
+CE}/${SMCLIB}/+${SOURCE}/${KENO}/+g;if ( not m+^${SOURCE}/+ ) {s+${SO
+URCE}/+\$$\{OBJECT\}/+g;print}' .depend ;\
${SCALE}/cmds/Sort .depend )
[download]

I have an understanding of the -n putting the code in a loop, the -i allowing to write to the same file, and the -e letting the command line act like code. I'm having trouble seeing what each Perl code "line" (the stuff between the ;'s) does, as well as if s+ was syntax for substitute or something else. If anyone can give a quick synopsis of what's going on I'd be quite grateful. Thanks!

~Jack

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Re: Command line question by kyle (Abbot) on Jun 17, 2008 at 21:51 UTC
Here it is spread out: `while (<>) { s+${SOURCE}/${SAMS}/++g; s+${SOURCE}/${SAMLIB}/++g; s+${SOURCE}/${SMCLIB}/+${SOURCE}/${KENO}/+g; if ( not m+^${SOURCE}/+ ) { s+${SOURCE}/+\$$\{OBJECT\}/+g; print } }` [download] This is run on a file named ".depend", and then something else runs after that. I'm guessing that `${SOURCE}` and friends are being interpolated somehow (even though they're in single quotes) because there's nothing in the Perl to give those variables values. Anyway, this is using "+" instead of "/" for the delimiters on `s///`, probably so that it can put a literal slash in there without having to backslash it. What it does (for each line) is something like: Remove "`${SOURCE}/${SAMS}/`" and "`${SOURCE}/${SAMLIB}/`" anywhere in the line. Replace every "`${SOURCE}/${SMCLIB}/`" with "`${SOURCE}/${KENO}/`" If the line starts with "`${SOURCE}/`", replace every "`${SOURCE}`" with a literal "`${OBJECT}`" (I think), and print the line. (Lines that don't start with "`${SOURCE}/`" are not printed and so removed.)	[reply] [d/l] [select]
Re^2: Command line question by ikegami (Patriarch) on Jun 17, 2008 at 23:39 UTC
I'm guessing that ${SOURCE} and friends are being interpolated somehow (even though they're in single quotes) Those quotes are processed by the shell. In the bourne shell or a derivative like bash, single quote don't perform any interpolation. `$ echo "${PATH}" .:/home/ikegami/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/gam +es $ echo '${PATH}' ${PATH}` [download] ( Here on end, assuming the bourne shell or a derivative like bash ) So Perl sees `BEGIN { $^I = ''; } while (<>) { s+${SOURCE}/${SAMS}/++g; s+${SOURCE}/${SAMLIB}/++g; s+${SOURCE}/${SMCLIB}/+${SOURCE}/${KENO}/+g; if ( not m+^${SOURCE}/+ ) { s+${SOURCE}/+\$$\{OBJECT\}/+g; print } }` [download] On the other hand, Perl regexp and replace expressions do interpolate. So the above is equivalent to `BEGIN { $^I = ''; } while (<>) { s+//++g; s+//++g; s+//+//+g; if ( not m+^/+ ) { s+/+\${OBJECT}/+g; print } }` [download] Depending on what the OP wants to do, he needs to use `-e""` instead of `-e''`, to escape the dollar signs, or to define those variables in Perl.	[reply] [d/l] [select]
Re^3: Command line question by parv (Parson) on Jun 18, 2008 at 00:48 UTC
My guess is that the code snippet is from a make file (while we are guessing).	[reply]
Re^3: Command line question by kyle (Abbot) on Jun 18, 2008 at 00:34 UTC
Ordinarily, I'd agree with you, but I get the impression that the OP's code works as-is, and he's just trying to figure out what it does and how. My guess is that the whole thing is in double quotes, and what perl actually sees is: `BEGIN { $^I = ""; } LINE: while (defined($_ = <ARGV>)) { s[value-of-SOURCE/value-of-SAMS/][]g; s[value-of-SOURCE/value-of-SAMLIB/][]g; s[value-of-SOURCE/value-of-SMCLIB/][value-of-SOURCE/value-of-KENO/ +]g; if (not m[^value-of-SOURCE/]) { s[value-of-SOURCE/][$${OBJECT}/]g; print $_; } }` [download] That `$${OBJECT}` in there still seems wrong, though, and the OP is ambiguous about whether this is working code or not, so I'm pretty far from sure about this.	[reply] [d/l] [select]
Re^4: Command line question by igotlongestname (Acolyte) on Jun 19, 2008 at 17:31 UTC
Re^5: Command line question by kyle (Abbot) on Jun 19, 2008 at 18:58 UTC
Re: Command line question by FunkyMonk (Bishop) on Jun 17, 2008 at 21:43 UTC
After removing some backslashes that shouldn't(?) be there, and running what's left through Deparse (`perl -MO=Deparse -c -e ...`), I got: `s[$SOURCE/$SAMS/][]g; s[$SOURCE/$SAMLIB/][]g; s[$SOURCE/$SMCLIB/][$SOURCE/$KENO/]g; if (not m[^$SOURCE/]) { s[$SOURCE/][$$OBJECT/]g; print $_; }` [download] Does that help? Unless I state otherwise, all my code runs with strict and warnings	[reply] [d/l] [select]