I have two Perl one liners:
perl -pe "s/\b$a\b/$b/g if m/param1 /" test
and
perl -pe "s/\b$a\b/$b/g unless /^#/" test
How can I combine theif m/somthing/ and the unless /something/, like:
[root#localhost tmp]# perl -pe "s/\b$a\b/$b/g if m/param1/ unless /^#/" test
syntax error at -e line 1, near "m/param1/ unless"
Maybe
perl -pe "s/\b$a\b/$b/g if m/param1/ && ! /^#/" test
does it.
unless is the same as if not. Judging by the way you've written the statement, I'm guessing you mean the following:
perl -pe "s/\b$a\b/$b/g if m/param1/ and not /^#/" test
(Although, you might have meant or instead of and?)
On an unrelated note, you may want to add the \Q and \E escape sequences around $a in your regex:
perl -pe "s/\b\Q$a\E\b/$b/g if m/param1 /" test
They escape any characters that are special to regexes. If you intend for $a to hold a regex you should probably move the word boundary assertions (\b) into it.
No matter what you choose to do, you will need to be careful with values in $a and $b. For instance:
a="/"
b="slash"
perl -pe "s/\b\Q$a\E\b/$b/g if m/param1 /" test
will cause a syntax error. One solution to this is to not use environment variables to replace code. Perl allows you access to the environment through the %ENV hash:
perl -pe 's/\b\Q$ENV{a}\E\b/$ENV{b}/g if m/param1 /' test
Notice the use of single ticks to avoid treating $ENV as a shell variable.
Related
Could command lines parameters been saved to a file and then pass the file to perl to parse out the options? Like response file (prefix the name with #) for some Microsoft tools.
I am trying to pass expression to perl via command line, like perl -e 'print "\n"', and Windows command prompt makes using double quotes a little hard.
There are several solutions, from most to least preferable.
Write your program to a file
If your one liner is too big or complicated, write it to a file and run it. This avoids messing with shell escapes. You can reuse it and debug it and work in a real editor.
perl path\to\some_program
Command line options to perl can be put on the otherwise useless on Windows #! line. Here's an example.
#!/usr/bin/perl -i.bak -p
# -i.bak Backs up the file.
# -p Puts each line into $_ and writes out the new value of $_.
# So this changes all instances in a file of " with '.
s{"}{'}g;
Use alternative quote delimiters
Perl has a slew of alternative ways to write quotes. Use them instead. This is good for both one liners as well as things like q[<tag key='value'>].
perl -e "print qq[\n]"
Escape the quote
^ is the cmd.exe escape character. So ^" is treated as a literal quote.
perl -e "print ^"\n^""
Pretty yucky. I'd prefer using qq[] and reserve ^" for when you need to print a literal quote.
perl -e "print qq[^"\n]"
Use the ASCII code
The ASCII and UTF-8 hex code for " is 22. You can supply this to Perl with qq[\x22].
perl -e "print qq[\x22\n]"
You can read the file into a string and then use
use Getopt::Long qw(GetOptionsFromString);
$ret = GetOptionsFromString($string, ...);
to parse the options from that.
I have several bash scripts that need to be modified and I would very much prefer to not do it by hand... basically, they all contain the line
for ((i=${BEGIN} ; i < ${END} ; i++))
and I need to change this to
for ((i=${BEGIN}-1 ; i < ${END} ; i++))
the i=${BEGIN} is unique and appears only once in each file, so I figured I could search and replace it using a simple perl command. What I came up with is
> perl -w -i -p -e "s/i=\$\{BEGIN\}/i=\$\{BEGIN\}-1/" Script.sh
which results in the following error
syntax error at -e line 1, near "{BEGIN"
syntax error at -e line 1, near "}continue"
Execution of -e aborted due to compilation errors.
What is the syntax error here?
Thanks!
Tsadkiel
Use apostrophes instead of double quotes:
perl -w -i -p -e 's/i=\$\{BEGIN\}/i=\$\{BEGIN\}-1/'
This way, backslashes aren't removed by shell, so perl sees them and they escape what they should escape.
The bash shell is performing interpolation on the argument "s/i=\$\{BEGIN\}/i=\$\{BEGIN\}-1/" before it gets to Perl. Let's see how that might work:
$ echo "s/i=\$\{BEGIN\}/i=\$\{BEGIN\}-1/"
s/i=$\{BEGIN\}/i=$\{BEGIN\}-1/
The substitution s/i=$\{BEGIN\}/i=$\{BEGIN\}-1/ is going to be a problem in Perl because Perl will treat the sequence $\{ as the start of a lookup on the hash variable %\, but it will fail to compile because it won't find an (unescaped) closing brace. So what you really want Perl to see is something like
s/i=\$\{BEGIN\}/i=\$\{BEGIN\}-1/
And there are at least two ways to change your original command-line to accomplish this:
Escape the dollar signs:
perl -wpi -e "s/i=\\\$\{BEGIN\}/i=\\\$\{BEGIN\}-1/"
Prefer single quotes, which aren't interpolated in bash:
perl -wpi -e 's/i=\$\{BEGIN\}/i=\$\{BEGIN\}-1/'
I am calling a perl one-liner inside a Perl script.
The intention of the one-liner is to remove the trailing space from a file.
Inside the main perl script:
`perl -pi -e 's/\s+$//' tape.txt`;
Now it is throwing me an error Substitution replacement not terminated at -e line 2.
Where is it going wrong?
It's because of the $/ (special variable) inside your main perl script. Note that variables are interpolated inside `` strings just like inside "" strings, and the fact that there are some single quotes in there doesn't change that. You need to escape that $:
`perl -pi -e 's/\s+\$//' tape.txt;`
The backtick syntax invokes a shell and when invoked, the shell assumes it should interpolate the string passed.
A cleaner syntax might be:
system('perl -pli -e "s/\s*$//" tape.txt');
Since you aren't capturing the output of the command, using backticks or qx in lieu of system isn't an issue.
Too, adding the -l switch autochomps each line read and then adds a newline back --- probably what you want.
\s matches [ \t\n\r\f] and do not want to match \n.
Notice use of {} for subst delimiters:
$ echo -e 'hi \nbye'| perl -pe 's{[\t\040]+$}{};' | cat -A
hi$
bye$
I have been using Linux env and recently migrated to solaris. Unfortunately one of my bash scripts requires the use of grep with the P switch [ pcre support ] .As Solaris doesnt support the pcre option for grep , I am obliged to find another solution to the problem.And pcregrep seems to have an obvious loop bug and sed -r option is unsupported !
I hope that using perl or nawk will solve the problem on solaris.
I have not yet used perl in my script and am unware neither of its syntax nor the flags.
Since it is pcre , I beleive that a perl scripter can help me out in a matter of minutes. They should match over multiple lines .
Which one would be a better solution in terms of efficiency the awk or the perl solution ?
Thanks for the replies .
These are some grep to perl conversions you might need:
grep -P PATTERN FILE(s) ---> perl -nle 'print if m/PATTERN/' FILE(s)
grep -Po PATTERN FILE(s) ---> perl -nle 'print "$1\n" while m/(PATTERN)/g' FILE(s)
That's my guess as to what you're looking for, if grep -P is out of the question.
Here's a shorty:
grep -P /regex/ ====> perl -ne 'print if /regex/;'
The -n takes each line of the file as input. Each line is put into a special perl variable called $_ as Perl loops through the whole file.
The -e says the Perl program is on the command line instead of passing it a file.
The Perl print command automatically prints out whatever is in $_ if you don't specify for it to print out anything else.
The if /regex/ matches the regular expression against whatever line of your file is in the $_ variable.
I want to wrap a Perl one-liner in a batch file. For a (trivial) example, in a Unix shell, I could quote up a command like this:
perl -e 'print localtime() . "\n"'
But DOS chokes on that with this helpful error message:
Can't find string terminator "'" anywhere before EOF at -e line 1.
What's the best way to do this within a .bat file?
For Perl stuff on Windows, I try to use the generalized quoting as much as possible so I don't get leaning toothpick syndrome. I save the quotes for the stuff that DOS needs:
perl -e "print scalar localtime() . qq(\n)"
If you just need a newline at the end of the print, you can let the -l switch do that for you:
perl -le "print scalar localtime()"
For other cool things you can do with switches, see the perlrun documentation.
In Windows' "DOS prompt" (cmd.exe) you need to use double quotes not single quotes. For inside the quoted Perl code, Perl gives you a lot of options. Three are:
perl -e "print localtime() . qq(\n)"
perl -e "print localtime() . $/"
perl -le "print ''.localtime()"
If you have Perl 5.10 or newer:
perl -E "say scalar localtime()"
Thanks to J.F. Sebastian's comment.
For general batch files under Windows NT+, the ^ character escapes lots of things (<>|&), but for quotes, doubling them works wonders:
C:\>perl -e "print localtime() . ""\n"""
Thu Oct 2 09:17:32 2008
First, any answer you get to this is command-specific, because the DOS shell doesn't parse the command-line like a uniq one does; it passes the entire unparsed string to the command, which does any splitting. That said, if using /subsystem:console the C runtime provides splitting before calling main(), and most commands use this.
If an application is using this splitting, the way you type a literal double-quote is by doubling it. So you'd do
perl -e "print localtime() . ""\n"""
In DOS, you use the "" around your Perl command. The DOS shell doesn't do single quotes like the normal Unix shell:
perl -e "print localtime();"