Menu
I am starting to lern Perl. I tried
perl -e 'print "The value of \$x=$x\n";'
gives:
The value of $x=
whereas:
perl -s -x=10 -e 'print "The value of \$x=$x\n";'
gives
No Perl script found in input
I would like to use the -s switch together with -e switch.. Why is it not working?
835
Perl does not support the use of switch statements. A switch statement allows a variable to be tested against a set list of values. In Perl, the equivalent of the switch statement is the given-when syntax. We state the values as given-when .
The switch statement takes a single scalar argument of any type, specified in parentheses. The value is followed by a block, which may contain one or more case statement followed by a block of Perl statement(s).
The most commonly used special variable is $_, which contains the default input and pattern-searching string. For example, in the following lines − #!/usr/bin/perl foreach ('hickory','dickory','doc') { print $_; print "\n"; }
Arguments to the script itself should come after the script, regardless of whether it's a one-liner or a file. While not always necessary, you can separate the arguments for perl from the arguments to your script with a --:
$ perl -s -E'say "\$x=$x"' -- -x=42
x=42
Ending the arguments to perl with -- is necessary because -x is a flag understood by perl itself, so your script would never see it. From perldoc perlrun:
-x
-xdirectory
tells Perl that the program is embedded in a larger chunk of unrelated text, such as in a mail message. Leading garbage will be discarded until the first line that starts with "#!" and contains the string "perl". Any meaningful switches on that line will be applied.
[…]
If a directory name is specified, Perl will switch to that directory before running the program. The -x switch controls only the disposal of leading garbage. The program must be terminated with "END" if there is trailing garbage to be ignored; the program can process any or all of the trailing garbage via the "DATA" filehandle if desired.
The directory, if specified, must appear immediately following the -x with no intervening whitespace.
As the specified input print "The value of \$x=$x\n"; does not contain a shebang, the actual script wasn't found and thus the error you encountered was emitted.
Do not use -s switch parsing for any but the most simple one-liners. Use Getopt::Long instead.
68
perl -se 'print "The value of \$x=$x\n";' -- -x=10
perlrun documentation could be more clear on this option,
-s enables rudimentary switch parsing for switches on the command line after the program name but before any filename arguments (or before an argument of --). Any switch found there is removed from @ARGV and sets the corresponding variable in the Perl program. The following program prints "1" if the program is invoked with a -xyz switch, and "abc" if it is invoked with -xyz=abc.
45
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
