ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
7.9. Modifying a File in Place with -i SwitchProblemYou need to modify a file in place from the command line, and you're too lazy[5] for the file manipulation of Recipe 7.8.
SolutionUse the -i and -p switches to Perl. Write your program on the command line: % perl -i.orig -p -e 'FILTER COMMAND' file1 file2 file3 ... Or use the switches in programs: #!/usr/bin/perl -i.orig -p # filter commands go here DiscussionThe -i command-line switch modifies each file in place. It creates a temporary file as in the previous recipe, but Perl takes care of the tedious file manipulation for you. Use it with -p (explained in Recipe 7.7) to turn: % perl -pi.orig -e 's/DATE/localtime/e' into: while (<>) { if ($ARGV ne $oldargv) { # are we at the next file? rename($ARGV, $ARGV . '.orig'); open(ARGVOUT, ">$ARGV"); # plus error check select(ARGVOUT); $oldargv = $ARGV; } s/DATE/localtime/e; } continue{ print; } select (STDOUT); # restore default output The -i switch takes care of making a backup (say The preceding one-liner would turn a file containing the following: Dear Sir/Madam/Ravenous Beast, As of DATE, our records show your account is overdue. Please settle by the end of the month. Yours in cheerful usury, --A. Moneylender into: Dear Sir/Madam/Ravenous Beast, As of Sat Apr 25 12:28:33 1998, our records show your account is overdue. Please settle by the end of the month. Yours in cheerful usury, --A. Moneylender This switch makes in-place translators a lot easier to write and to read. For instance, this changes isolated instances of % perl -i.old -pe 's{\bhisvar\b}{hervar}g' *.[Cchy] Turn on and off the -i behavior with the special variable # set up to iterate over the *.c files in the current directory, # editing in place and saving the old file with a .orig extension local $^I = '.orig'; # emulate -i.orig local @ARGV = glob("*.c"); # initialize list of files while (<>) { if ($. == 1) { print "This line should appear at the top of each file\n"; } s/\b(p)earl\b/${1}erl/ig; # Correct typos, preserving case print; } continue {close ARGV if eof} Beware that creating a backup file under a particular name when that name already exists clobbers the previously backed up version. See Alsoperlrun (1), and the "Switches" section of Chapter 6 of Programming Perl; the |