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Table of Contents
Perl
Some one liners: socher.org
Oneliners
To change only the fifth line, you can add a test checking $., the input line number, then only perform the operation when the test passes:
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To add lines before a certain line, you can add a line (or lines!) before Perl prints $_:
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You can even add a line to the beginning of a file, since the current line prints at the end of the loop:
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To insert a line after one already in the file, use the -n switch. It's just like -p except that it doesn't print $_ at the end of the loop, so you have to do that yourself. In this case, print $_ first, then print the line that you want to add.
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To delete lines, only print the ones that you want.
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… or …
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Using %ENV to pass parameters to a perl one-liner
Used here to clean up a comma-separated list of parameters passed into a shell.<br />
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Add a line after another one in a file using Perl
Use Perl to filter a script (or a load of scripts) and add an extra line when certain pattern match condition exists.<br /> Uses -n switch with print because using -p switch evaluates your condition first and then prints the line. This could be used if you want to print a line before the matched line!
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perl -a
Turns on autosplit mode. Use -F<delim> to specify how to split the elements<br /> Breaks down the input into elements of an automatically assigned array called @F.
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perl -l
When trimming whitespace from your input, the \n is removed also. Using -l adds it back in at the end of processing.<br /> See examples above.
BEGIN and END
Allows you to run code before or after the loop over the lines.<br /> Example, sum the values in the second column of a CSV file…<br /> Replace the 'n' with a 'p' to see the numbers being summed.
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.. operater
Cut chunks out of a file from /start range marker/ .. /end range marker/
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A one-liner web server!
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- First we accept a socket and fork the server. Then we overload the new socket as a code ref. This code ref takes one argument, another code ref, which is used as a callback.
- The callback is called once for every line read on the socket. The line is put into $_ and the socket itself is passed in to the callback.
- Our callback is scanning the line in $_ for an HTTP GET request. If one is found it parses the file name into $1. Then we use $1 to create an new IO::All file object… with a twist. If the file is executable(“-x”), then we create a piped command as our IO::All object. This somewhat approximates CGI support.
- Whatever the resulting object is, we direct the contents back at our socket which is in $_0.
From: commandlinefu.com
What Perl modules are installed?
As found by typing “perldoc q installed”
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Prepend a line at the beginning of a file
Surprisingly tricky thing to do as a one-liner. Seemingly cannot be done (cross-platform) in ksh in one line.
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Implement a socket client/server in Perl
Scan for emails with attachments and save attachments to files
Install a Perl module from CPAN
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Print out the first and last words of all lines in a file
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Print only the lines in a file between 2 search patterns
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Mass update of files using perl inline script
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Perl emulation of dos2unix command
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and then back again with unix2dos
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Print a file except / excluding certain lines
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Exclude the first few lines of a file
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Delete the last line of a file
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Print lines between 2 markers in a file
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Print lines not between 2 markers in a file!
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Print a few lines in a file
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but more efficiently…
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Print lines of a file in reverse order
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Print characters in lines of a file in reverse order
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Find palindromes in a file
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Reverse all the characters in a file
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Reverse all the characters in a paragraph but keeping the paragraphs in order
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Trim all heading and trailing spaces and compress any intermediate spaces to 1
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Nice one to reformat a document so that all lines are between 50 and 70 characters long. Only breaks on whitespace
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Substitute text in subject placing modified text in result
Variable “subject” remains unchanged
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Print balancing quotes
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Capitalise all words in a file (ensuring all others letters in the words are lower case)
ref: Matz Kindahl
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Translate into Zafir language!
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Read in (include) a configuration file in Perl
Although there are several ways to “include” files into the current program, this method is the simplest.<br /> The problem with using require or include is that the scope is different so any my variables won't be visible<br /> The trick here is the use of the “our” hash.
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Send an email from perl without needing any external modules
but it only works on Unix :(
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Using the function is straightforward. Simply pass it the data in the correct order.
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What "day of the year" (DOY) number was it yesterday?
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What "day of the year" (DOY) number is it today?
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Sort a list
Numerically
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Alphabetically
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Alphabetically (case-insensitive)
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Schwartzian transform
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broken down into (semi)understandable pieces looks like this…
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Use 'map' to apply transformations
Push the list in one side (right) and get it back on the other (left) with some transformation applied.<br /> Inside the code block, you refer to the current element with the traditional $_ variable.
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Use it with join to create clever stuff…
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Difference in hours between two dates
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or, without using any external modules…
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Slurp an external file into a variable
The idea is to read an SQL file into a variable to prepare and execute it
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Search for a (list of) keyword(s) in a file
Could write this in several loops but here is a very neat way. Spotted on Stackoverflow.com
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basically it builds up a regular expression and searches for it.<br /> See reference link for more details.<br /><br /> Can also be done very neatly with grep in shell<br />
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where keywords.txt is a file containing the list of words to search for.
Assign and substitute a value to a variable in one statement
Keep forgetting where the parentheses go so have to write it down…<br /> Have to pre-define the variable $new_var otherwise you will get:
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Match a regular expression across multiple lines
I always forget this regex and it's sooo useful!
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where backup.ini looks like this:
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Using /s and /m modifiers in a regular expression
Tom Christiansen in his Perl Cookbook demonstrates the difference between these 2 confusing modifiers
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Match regular expression and assign to a variable in a single step
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or split directory and filenames (on Windows or Unix)
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or split a line into bits and assign the bits to variables
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Perl ternary operator
Putting examples here as I keep forgetting the syntax/semantics!<br /> Theoretically it should be:
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which to me means:
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but it's not like that, it's like this:
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and this
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Extract a value from a comma separated list of values in Perl
Suppose you need the 10th column …but only from the lines ending in 'detail'
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or
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and print out the 10th element of @fields
Typical filter program (without needing to slurp)
Keep one of these here to save me looking it up all the time!
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