Escaping perl 中的括号 bash 命令的反引号

Question

I have been using backticks for years but this is the first time I have tried using a command with a parentheses. I am getting an error that I cannot figure out.

I have tried putting in double quotes and escaping with the \ in multiple places, but nothing seems to work. Any help would be appreciated.

COMMAND the $file5 and $file6 are perl variables, not bash.

@array = `/usr/bin/join -j 1 -t, <(cat $file5 | awk -F, '{print \$3","\$1}' | sort) <( cat $file6 | awk -F, '{print \$3","\$1}' | sort) `

ERROR: AH01215: sh: -c: line 0: syntax error near unexpected token `(', referer:

Answer 1

Backticks use /bin/sh , and while <(... ) is something recognized by bash , it's not recognized by the bourne shell. If you use backticks, you will need to use

my $bash_cmd = ...;
my @lines = `bash -c $bash_cmd`;

Building sh and bash shell commands can be done using String::ShellQuote .

use String::ShellQuote qw( shell_quote );

my $file5_quoted = shell_quote($file5);
my $file6_quoted = shell_quote($file6);

my $awk_cmd = shell_quote("awk", "-F,", '{print $3","$1}');

my $bash_cmd = '/usr/bin/join -j 1 -t,'
   . " <( $awk_cmd $file5_quoted | sort )"
   . " <( $awk_cmd $file6_quoted | sort )";

my $sh_cmd = shell_quote("bash", "-c", $bash_cmd);
my @lines = `$sh_cmd`;

We can use IPC::System::Simple 's capturex to avoid launching more shells than needed, as well as to provide error checking. To do this, replace the last two lines of the above with the following:

use IPC::System::Simple qw( capturex );

my @lines = capturex("bash", "-c", $bash_cmd);

Answer 2

One workaround is to create a shell script that accepts the two filenames from perl, processes the join using those two input files, and return the result to the perl array.

#1. Create join.sh that contains these four lines:

    cat $1 | awk -F, '{print $3","$1}' | sort > 1.out
    cat $2 | awk -F, '{print $3","$1}' | sort > 2.out
    /usr/bin/join -j 1 -t, 1.out 2.out
    rm 1.out 2.out


#2. Modify your perl statement to call join.sh as follows:

    @array=`join.sh $file5 $file6`;