I have an utility to generate code documentation every night. I would like to add a timestamp in order to be aware how old the generated documentation is. I would like to use perl.
I've seen that with the following sentence I can change a joker (%1) by any value I want
perl -pi.bak -e 's/%1/date/g' footer.html
And with this other one I can get the system timestamp:
perl -MPOSIX -we "print POSIX::strftime('%d/%m/%Y %H:%M:%S', localtime)"
My question is whether there is any way to merge both instructions in just one sentence.
Thank you very much
Try doing this :
perl -MPOSIX -pi.bak -e 'BEGIN{$date = strftime("%d/%m/%Y %H:%M:%S", localtime);} s/%1/$date/g' file.html
sh command:
perl -i.bak -MPOSIX -pe's/%1/strftime("%d/%m/%Y %H:%M:%S", localtime)/eg'
cmd command:
perl -i.bak -MPOSIX -pe"s/%1/strftime('%d/%m/%Y %H:%M:%S', localtime)/eg"
/e cause the replacement expression to be treated as Perl code to execute, the result of which is the replacement text.
Related
What is the equivalent Perl command to the GNU coreutils command readlink -f?
If any component of the file name except the last one is missing or unavailable, readlink produces no
output and exits with a nonzero exit code. A trailing slash is
ignored.
You can use Cwd:
use Cwd 'abs_path';
my $path = "/some/arbitrary/path";
print abs_path($path);
Test:
for q in exists imaginary imarginary/imaginary ; do
echo "$q"
echo -n "readlink -f: " ; readlink -f "$q"
echo -n "abs_path: " ; perl -MCwd=abs_path -E'say abs_path $ARGV[0]' "$q"
echo
done
Output:
exists
readlink -f: /home/eric/exists
abs_path: /home/eric/exists
imaginary
readlink -f: /home/eric/imaginary
abs_path: /home/eric/imaginary
imaginary/imaginary
readlink -f: abs_path:
As a total Perl rookie, I'm happy to say I have figured out this STDIN solution all by myself (after several tries, remember that Perl's learning curve IS known to be steep).
devnull's solution was great with no doubt, but it was a little too "scriptish" for my taste - whereas I'd sometimes just want to pipe a perl one-liner to an echo'ed string, like this:
echo "/home/user/somesymlinkedpath" | perl -MCwd=abs_path -nle 'print abs_path $_'
So as there might be more people around who want to know about how to code this kind of piped form (making perl read the argument from STDIN), I've decided to post it here too.
This question already has answers here:
How can I process options using Perl in -n or -p mode?
(2 answers)
Closed last year.
I often need to run some Perl one-liners for fast data manipulations, like
some_command | perl -lne 'print if /abc/'
Reading from a pipe, I don't need a loop around the command arg filenames. How can I achieve the next?
some_command | perl -lne 'print if /$ARGV[0]/' abc
This gives the error:
Can't open abc: No such file or directory.
I understand that the '-n' does the
while(<>) {.... }
around my program, and the <> takes args as filenames, but doing the next every time is a bit impractical
#/bin/sh
while read line
do
some_command | perl -lne 'BEGIN{$val=shift #ARGV} print if /$val/' "$line"
done
Is there some better way to get "inside" the Perl ONE-LINER command line arguments without getting them interpreted as filenames?
Some solutions:
perl -e'while (<STDIN>) { print if /$ARGV[0]/ }' pat
perl -e'$p = shift; while (<>) { print if /$p/ }' pat
perl -e'$p = shift; print grep /$p/, <>' pat
perl -ne'BEGIN { $p = shift } print if /$p/' pat
perl -sne'print if /$p/' -- -p=pat
PAT=pat perl -ne'print if /$ENV{PAT}/'
Of course, it might make more sense to create a pattern that's an ORing or all patterns rather than executing the same command for each pattern.
Also reasonably short:
... | expr=abc perl -lne 'print if /$ENV{expr}/'
Works in bash shell but maybe not other shells.
It depends on what you think will be in the lines you read, but you could play with:
#/bin/sh
while read line
do
some_command | perl -lne "print if /$line/"
done
Clearly, if $line might contain slashes, this is not going to fly. Then, AFAIK, you're stuck with the BEGIN block formulation.
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 have a file that contains a lot of these
"/watch?v=VhsnHIUMQGM"
and I would like to output the letter code using a perl one-liner. So I try
perl -nle 'm/\"\/watch\?v=(.*?)\"/g' filename.txt
but it doesn't print anything.
What am I doing wrong?
The -n option processes each line but doesn't print anything out. So you need to add an explicit print if you successfully match.
perl -ne 'while ( m/\"\/watch\?v=(.+?)\"/g ) { print "$1\n" }' filename.txt
Another approach, if you're sure every line will match, is to use the -p option which prints out the value of $_ after processing, e.g.:
perl -pe 's/\"\/watch\?v=(.+?)\"/$1//' filename.txt
Your regex is fine. You're getting no output because the -n option won't print anything. It simply wraps a while (<>) { ... } loop around your program (run perl --help for brief explanations of the Perl options).
The following uses your regex, but add some printing. In list context, regexes with the /g option return all captures. Effectively, we print each capture.
perl -nle 'print for m/\"\/watch\?v=(.*?)\"/g' data.dat
You can split the string on "=" instead of matching:
perl -paF= -e '$_= #F[1]' filename.txt
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();"