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$
Related
I need to comment out a line in a crontab file through a script, so it contains directories, spaces and symbols. This specific line is stored in a variable and I am starting to get mixed up on how to escape the variable. Since the line changes on a regular basis I dont want any escaping in there. I don't want to simply add # in front of it, since I also need to switch it around and replace the line again with the original without the #.
So the goal is to replace $line with #$line (comment) with the possibility to do it the other way around (uncomment).
So I have a variable:
line="* * * hello/this/line & /still/this/line"
This is a line that occurs in a file, file.txt. Wich needs to get comment out.
First try:
sed -i "s/^${line}/#${line}/" file.txt
Second try:
sed -i 's|'${line}'|'"#${line}"'|g' file.txt
choroba's helpful answer shows an effective solution using perl.
sed solution
If you want to use sed, you must use a separate sed command just to escape the $line variable value, because sed has no built-in way to escape strings for use as literals in a regex context:
lineEscaped=$(sed 's/[^^]/[&]/g; s/\^/\\^/g' <<<"$line") # escape $line for use in regex
sed -i "s/^$lineEscaped\$/#&/" file.txt # Note the \$ to escape the end-of-line anchor $
With BSD/macOS sed, use -i '' instead of just -i for in-place updating without backup.
And the reverse (un-commenting):
sed -i "s/^#\($lineEscaped\)\$/\1/" file.txt
See this answer of mine for an explanation of the sed command used for escaping, which should work with any input string.
Also note how variable $lineEscaped is only referenced once, in the regex portion of the s command, whereas the substitution-string portion simply references what the regex matched (which avoids the need to escape the variable again, using different rules):
& in the substitution string represents the entire match, and \1 the first capture group (parenthesized subexpression, \(...\)).
For simplicity, the second sed command uses double quotes in order to embed the value of shell variable $lineEscaped in the sed script, but it is generally preferable to use single-quoted scripts so as to avoid confusion between what the shell interprets up front vs. what sed ends up seeing.
For instance, $ is special to both the shell and sed, and in the above script the end-of-line anchor $ in the sed regex must therefore be escaped as \$ to prevent the shell from interpreting it.
One way to avoid confusion is to selectively splice double-quoted shell-variable references into the otherwise single-quoted script:
sed -i 's/^'"$lineEscaped"'$/#&/' file.txt
awk solution
awk offers literal string matching, which obviates the need for escaping:
awk -v line="$line" '$0 == line { $0 = "#" $0 } 1' file.txt > $$.tmp && mv $$.tmp file.txt
If you have GNU Awk v4.1+, you can use -i inplace for in-place updating.
And the reverse (un-commenting):
awk -v line="#$line" '$0 == line { $0 = substr($0, 2) } 1' file.txt > $$.tmp &&
mv $$.tmp file.txt
Perl has ways to do the quoting/escaping for you:
line=$line perl -i~ -pe '$regex = quotemeta $ENV{line}; s/^$regex/#$ENV{line}/' -- input.txt
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 trying to find and replace a string in a xml document
This is the code I am using:
perl -pi -e s/xmlNamespaceAware=\"false\"">"/xmlNamespaceAware=\"false\"">""<"Alias">"hostname"<"/Alias">"/g
Error:
syntax error at -e line 1, near "s/xmlNamespaceAware="false">/xmlNamespaceAware="false"><Alias>webtctdm1.ecorp.cat.com</Alias"
If I remove the / in it works fine.
Also is there anyway I can write "<"Alias">"hostname"<"/Alias">" on a newline oppose to the same line as xmlNamespaceAware="false">
Thanks in advance.
Make your life easier and pick a delimiter other than / when dealing with HTML/XML.
With newline literal:
perl -pi -e '
s{xmlNamespaceAware="false">}
{xmlNamespaceAware="false">
<Alias>hostname</Alias>}g' *.xml
With newline escape character:
perl -pi -e '
s{xmlNamespaceAware="false">}
{xmlNamespaceAware="false">\n<Alias>hostname</Alias>}g' *.xml
Both do the same.
You can use the \K escape character for convenience. It will preserve the preceding string, much like a look-around assertion. I am also using # as the delimiter for the substitution regex to avoid having to escape slashes.
perl -pi -e 's#xmlNamespaceAware="false">\K#\n<Alias>hostname</Alias>#g'
That's a hopeless mess of a string. You've forgotten to escape some ", you've got a bare / in </Alias> which actually terminates the regex. Why not just use a single-quoted string to hold the whole thing?
perl -pi -e 's/xmlNamespaceAware="false">/xmlNamespaceAware="false"><Alias>hostname<\/Alias>/g'
I think this should do it for you, but I have no Linux box to hand to try it. Using pipe as a delimiter for s/// avoids the need for escaping slashes.
perl -pi -e 's|xmlNamespaceAware="false">|xmlNamespaceAware="false">\n<Alias>hostname</Alias>|g'
I've got windows bat file, (using activeperl)
#echo off
perl -p -e 's/DIV\[/div\[/g' orginal.txt > output.txt
perl -p -e 'rename("output.txt", "orginal.txt")';
...
Running a .bat file, and I just cant get it to run properly..
Can't open ;: No such file or directory, <> line 12248.
Can't find string terminator "'" anywhere before EOF at -e line 1.
Not sure what I'm doing wrong..
You can't use single-quotes to enclose the Perl code in Windows. As a result, you need to escape the double-quotes or find other alternatives, such as qq(...).
perl -pe "s/DIV\[/div\[/g" original.txt > output.txt
perl -pe "rename(qq(output.txt), qq/original.txt/)"
Note that in this case, the arguments to rename can simply be rename('a.txt', 'b.txt') since they are literals and no variable interpolation is required.
You ought to use double quotes to quote the program text under Windows cmd. In your example, you can just swiztch double and single quotes. In cases where you really need double quotes in the perl text, use qq{ .... } instead.
The other posters are correct: windows requires double quotes for -e scripts to perl, which often screws things up. There is one more thing you can do, though: Use the -i switch, like this:
#echo off
perl -pi.bak -we "s/DIV\[/div\[/g" original.txt
The -i.bak switch will edit the file in place - no rename required - AND it will store a backup of the file in "original.txt.bak". If you do not want a backup, remove the ".bak" part and just use -pi.