chomp 和 $/

【转】[Perl]chomp 和 $/

chomp用来去掉字符串结尾的空行,这是我之前的理解。

今天仔细看了chomp的文档,原来chomp不一定只用来删除字符串结尾的空行,它可以删除结尾的$/, 只不过$/的默认值是newline,所以给人的感觉chomp总是用来删除结尾的空行。

通过改变$/的默认值,可以让chomp变得更灵活。
比如你的某个变量$var结尾有多个空行,怎么删除呢?
可以:
$/="";
chomp($var);

如果$var的结尾是a,你想删除a, 
$/="a";
chomp($var);
再比如windows 文件换行符为”\r\n“,这时候可以:(但是记住!在后面针对linux文件继续用chomp的时候,一定要把$/改回来,即改成$/ = "\n")
$/="\r\n";
chomp;

=========================================

有网友说我的斜线写反了。查了查perlvar, 发现 $\ 和$/是两个不同的东西:
$/: The input record separator, newline by default.
$\: The output record separator for the print operator.
chomp:  removes any trailing string that corresponds to the current value of $/

发现后来别人给我的文件各种奇葩的格式都有,有的chomp之后行末还是会有空格。那么这个时候:
$_ =~ s/\s+$//;         #####将末尾的空格,换行符都去掉,可以代替chomp;而且更好用些。
#!/usr/bin/env perl # # Copyright (C) 2006 OpenWrt.org # Copyright (C) 2016 LEDE project # # This is free software, licensed under the GNU General Public License v2. # See /LICENSE for more information. # use strict; use warnings; use File::Basename; use File::Copy; use Text::ParseWords; @ARGV > 2 or die "Syntax: $0 <target dir> <filename> <hash> <url filename> [<mirror> ...]\n"; my $url_filename; my $target = glob(shift @ARGV); my $filename = shift @ARGV; my $file_hash = shift @ARGV; $url_filename = shift @ARGV unless $ARGV[0] =~ /:\/\//; my $scriptdir = dirname($0); my @mirrors; my $ok; my $check_certificate = $ENV{DOWNLOAD_CHECK_CERTIFICATE} eq "y"; $url_filename or $url_filename = $filename; sub localmirrors { my @mlist; open LM, "$scriptdir/localmirrors" and do { while (<LM>) { chomp $_; push @mlist, $_ if $_; } close LM; }; open CONFIG, "<".$ENV{'TOPDIR'}."/.config" and do { while (<CONFIG>) { /^CONFIG_LOCALMIRROR="(.+)"/ and do { chomp; my @local_mirrors = split(/;/, $1); push @mlist, @local_mirrors; }; } close CONFIG; }; my $mirror = $ENV{'DOWNLOAD_MIRROR'}; $mirror and push @mlist, split(/;/, $mirror); return @mlist; } sub which($) { my $prog = shift; my $res = `command -v $prog`; $res or return undef; return $res; } sub hash_cmd() { my $len = length($file_hash); my $cmd; $len == 64 and return "$ENV{'MKHASH'} sha256"; $len == 32 and return "$ENV{'MKHASH'} md5"; return undef; } sub download_cmd($) { my $url = shift; my $have_curl = 0; if (open CURL, "curl --version 2>/dev/null |") { if (defined(my $line = readline CURL)) { $have_curl = 1 if $line =~ /^curl /; } close CURL; } return $have_curl ? (qw(curl -k -f --connect-timeout 20 --retry 5 --location), $check_certificate ? () : '--insecure', shellwords($ENV{CURL_OPTIONS} || ''), $url) : (qw(wget --tries=5 --timeout=20 --output-document=-), $check_certificate ? () : '--no-check-certificate', shellwords($ENV{WGET_OPTIONS} || ''), $url) ; } my $hash_cmd = hash_cmd(); $hash_cmd or ($file_hash eq "skip") or die "Cannot find appropriate hash command, ensure the provided hash is either a MD5 or SHA256 checksum.\n"; sub download { my $mirror = shift; my $download_filename = shift; $mirror =~ s!/$!!; if ($mirror =~ s!^file://!!) { if (! -d "$mirror") { print STDERR "Wrong local cache directory -$mirror-.\n"; cleanup(); return; } if (! -d "$target") { system("mkdir", "-p", "$target/"); } if (! open TMPDLS, "find $mirror -follow -name $filename 2>/dev/null |") { print("Failed to search for $filename in $mirror\n"); return; } my $link; while (defined(my $line = readline TMPDLS)) { chomp ($link = $line); if ($. > 1) { print("$. or more instances of $filename in $mirror found . Only one instance allowed.\n"); return; } } close TMPDLS; if (! $link) { print("No instances of $filename found in $mirror.\n"); return; } print("Copying $filename from $link\n"); copy($link, "$target/$filename.dl"); $hash_cmd and do { if (system("cat '$target/$filename.dl' | $hash_cmd > '$target/$filename.hash'")) { print("Failed to generate hash for $filename\n"); return; } }; } else { my @cmd = download_cmd("$mirror/$download_filename"); print STDERR "+ ".join(" ",@cmd)."\n"; open(FETCH_FD, '-|', @cmd) or die "Cannot launch curl or wget.\n"; $hash_cmd and do { open MD5SUM, "| $hash_cmd > '$target/$filename.hash'" or die "Cannot launch $hash_cmd.\n"; }; open OUTPUT, "> $target/$filename.dl" or die "Cannot create file $target/$filename.dl: $!\n"; my $buffer; while (read FETCH_FD, $buffer, 1048576) { $hash_cmd and print MD5SUM $buffer; print OUTPUT $buffer; } $hash_cmd and close MD5SUM; close FETCH_FD; close OUTPUT; if ($? >> 8) { print STDERR "Download failed.\n"; cleanup(); return; } } $hash_cmd and do { my $sum = `cat "$target/$filename.hash"`; $sum =~ /^(\w+)\s*/ or die "Could not generate file hash\n"; $sum = $1; if ($sum ne $file_hash) { print STDERR "Hash of the downloaded file does not match (file: $sum, requested: $file_hash) - deleting download.\n"; cleanup(); return; } }; unlink "$target/$filename"; system("mv", "$target/$filename.dl", "$target/$filename"); cleanup(); } sub cleanup { unlink "$target/$filename.dl"; unlink "$target/$filename.hash"; } @mirrors = localmirrors(); foreach my $mirror (@ARGV) { if ($mirror =~ /^\@SF\/(.+)$/) { # give sourceforge a few more tries, because it redirects to different mirrors for (1 .. 5) { push @mirrors, "https://downloads.sourceforge.net/$1"; } } elsif ($mirror =~ /^\@OPENWRT$/) { # use OpenWrt source server directly } elsif ($mirror =~ /^\@DEBIAN\/(.+)$/) { push @mirrors, "https://ftp.debian.org/debian/$1"; push @mirrors, "https://mirror.leaseweb.com/debian/$1"; push @mirrors, "https://mirror.netcologne.de/debian/$1"; } elsif ($mirror =~ /^\@APACHE\/(.+)$/) { push @mirrors, "https://mirror.netcologne.de/apache.org/$1"; push @mirrors, "https://mirror.aarnet.edu.au/pub/apache/$1"; push @mirrors, "https://mirror.csclub.uwaterloo.ca/apache/$1"; push @mirrors, "https://archive.apache.org/dist/$1"; push @mirrors, "http://mirror.cogentco.com/pub/apache/$1"; push @mirrors, "http://mirror.navercorp.com/apache/$1"; push @mirrors, "http://ftp.jaist.ac.jp/pub/apache/$1"; push @mirrors, "ftp://apache.cs.utah.edu/apache.org/$1"; push @mirrors, "ftp://apache.mirrors.ovh.net/ftp.apache.org/dist/$1"; } elsif ($mirror =~ /^\@GITHUB\/(.+)$/) { # give github a few more tries (different mirrors) for (1 .. 5) { push @mirrors, "https://raw.githubusercontent.com/$1"; } } elsif ($mirror =~ /^\@GNU\/(.+)$/) { push @mirrors, "https://mirror.csclub.uwaterloo.ca/gnu/$1"; push @mirrors, "https://mirror.netcologne.de/gnu/$1"; push @mirrors, "http://ftp.kddilabs.jp/GNU/gnu/$1"; push @mirrors, "http://www.nic.funet.fi/pub/gnu/gnu/$1"; push @mirrors, "http://mirror.internode.on.net/pub/gnu/$1"; push @mirrors, "http://mirror.navercorp.com/gnu/$1"; push @mirrors, "ftp://mirrors.rit.edu/gnu/$1"; push @mirrors, "ftp://download.xs4all.nl/pub/gnu/$1"; push @mirrors, "https://ftp.gnu.org/gnu/$1"; } elsif ($mirror =~ /^\@SAVANNAH\/(.+)$/) { push @mirrors, "https://mirror.netcologne.de/savannah/$1"; push @mirrors, "https://mirror.csclub.uwaterloo.ca/nongnu/$1"; push @mirrors, "http://ftp.acc.umu.se/mirror/gnu.org/savannah/$1"; push @mirrors, "http://nongnu.uib.no/$1"; push @mirrors, "http://ftp.igh.cnrs.fr/pub/nongnu/$1"; push @mirrors, "ftp://cdimage.debian.org/mirror/gnu.org/savannah/$1"; push @mirrors, "ftp://ftp.acc.umu.se/mirror/gnu.org/savannah/$1"; } elsif ($mirror =~ /^\@KERNEL\/(.+)$/) { my @extra = ( $1 ); if ($filename =~ /linux-\d+\.\d+(?:\.\d+)?-rc/) { push @extra, "$extra[0]/testing"; } elsif ($filename =~ /linux-(\d+\.\d+(?:\.\d+)?)/) { push @extra, "$extra[0]/longterm/v$1"; } foreach my $dir (@extra) { push @mirrors, "https://cdn.kernel.org/pub/$dir"; push @mirrors, "https://download.xs4all.nl/ftp.kernel.org/pub/$dir"; push @mirrors, "https://mirrors.mit.edu/kernel/$dir"; push @mirrors, "http://ftp.nara.wide.ad.jp/pub/kernel.org/$dir"; push @mirrors, "http://www.ring.gr.jp/archives/linux/kernel.org/$dir"; push @mirrors, "ftp://ftp.riken.jp/Linux/kernel.org/$dir"; push @mirrors, "ftp://www.mirrorservice.org/sites/ftp.kernel.org/pub/$dir"; } } elsif ($mirror =~ /^\@GNOME\/(.+)$/) { push @mirrors, "https://download.gnome.org/sources/$1"; push @mirrors, "https://mirror.csclub.uwaterloo.ca/gnome/sources/$1"; push @mirrors, "http://ftp.acc.umu.se/pub/GNOME/sources/$1"; push @mirrors, "http://ftp.kaist.ac.kr/gnome/sources/$1"; push @mirrors, "http://www.mirrorservice.org/sites/ftp.gnome.org/pub/GNOME/sources/$1"; push @mirrors, "http://mirror.internode.on.net/pub/gnome/sources/$1"; push @mirrors, "http://ftp.belnet.be/ftp.gnome.org/sources/$1"; push @mirrors, "ftp://ftp.cse.buffalo.edu/pub/Gnome/sources/$1"; push @mirrors, "ftp://ftp.nara.wide.ad.jp/pub/X11/GNOME/sources/$1"; } else { push @mirrors, $mirror; } } push @mirrors, 'https://sources.cdn.openwrt.org'; push @mirrors, 'https://sources.openwrt.org'; push @mirrors, 'https://mirror2.openwrt.org/sources'; if (-f "$target/$filename") { $hash_cmd and do { if (system("cat '$target/$filename' | $hash_cmd > '$target/$filename.hash'")) { die "Failed to generate hash for $filename\n"; } my $sum = `cat "$target/$filename.hash"`; $sum =~ /^(\w+)\s*/ or die "Could not generate file hash\n"; $sum = $1; cleanup(); exit 0 if $sum eq $file_hash; die "Hash of the local file $filename does not match (file: $sum, requested: $file_hash) - deleting download.\n"; unlink "$target/$filename"; }; } while (!-f "$target/$filename") { my $mirror = shift @mirrors; $mirror or die "No more mirrors to try - giving up.\n"; download($mirror, $url_filename); if (!-f "$target/$filename" && $url_filename ne $filename) { download($mirror, $filename); } } $SIG{INT} = \&cleanup; 针对每次整编都会再次下载一遍dl目录下的包,以上代码中是否体现出了这一点
07-15
翻译代码#####################Find the relevant software in the systerm######################## my $nucmer="/usr/bin/nucmer"; my $deltaFilter="/usr/bin/delta-filter"; my $showcoords="/usr/bin/show-coords"; my $minimap2="/usr/bin/minimap2"; if (($MappingSoft eq "mummer") or ($MappingSoft eq "nucmer")) { # mummer-4.0.0/bin/nucmer # mummer-4.0.0/bin/delta-filter # mummer-4.0.0/bin/show-coords if ( !(-e $nucmer) ) { $nucmer=`which nucmer 2> /dev/null `;chomp $nucmer; } if ( !(-e $deltaFilter) ) { $deltaFilter=`which delta-filter 2> /dev/null `;chomp $deltaFilter; } if ( !(-e $showcoords) ) { $showcoords=`which show-coords 2> /dev/null `;chomp $showcoords; } if (defined $BinDir) { my $tmp="$BinDir/nucmer"; if (-e $tmp) {$nucmer=$tmp;} $tmp="$BinDir/delta-filter"; if (-e $tmp) {$deltaFilter=$tmp;} $tmp="$BinDir/show-coords"; if (-e $tmp) {$showcoords=$tmp;} } if ( !(-e $showcoords) ) { print "\tCan't find the mummer [show-coords] at \$PATH or \$BinDir\n"; print "\tplease Check at it\n";exit; } if ( !(-e $deltaFilter) ) { print "\tCan't find the mummer [delta-Filter] at \$PATH or \$BinDir\n"; print "\tplease Check at it\n";exit; } if ( !(-e $nucmer) ) { print "\tCan't find the mummer [nucmer] at \$PATH or \$BinDir\n"; print "\tplease Check at it\n";exit; } my $NumVer=`$nucmer -V `; chomp $NumVer ; my @ccc=split /\./,$NumVer; if ($ccc[0] <4 ) { print "found the $nucmer version is $NumVer < 4.0 , we need the 4.0\n"; print "\tplease Check at it\n";exit; } } else { if ( !(-e $minimap2) ) { $minimap2=`which minimap2 2> /dev/null `;chomp $minimap2; } if (defined $BinDir) { my $tmp="$BinDir/minimap2"; if (-e $tmp) {$minimap2=$tmp;} } if ( !(-e $minimap2) ) { print "\tCan't find the [ minimap2 ] at \$PATH or \$BinDir\n"; print "\tplease Check at it\n";exit; } } my $NGenomeSyn="$Bin/../NGenomeSyn"; if ( !(-e $NGenomeSyn) ) { $NGenomeSyn="$Bin/NGenomeSyn"; if ( !(-e $NGenomeSyn) ) { print "\tCan't find the [NGenomeSyn] at [ $Bin/..]\n"; print "\tplease Check at it\n";exit; } }
06-09
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