I'm parsing a crash log using perl and I want to extract the backtrace component. I obtain the log file using the following command:
$log = `adb shell 'ls -d ./tombstones/*' |grep tombstone_ | tr '\r' ' ' | tail -n1 | xargs adb shell cat`;
(I'm not familiar with perl, as you can see)
I would like to scan the resulting variable (log) for backtrace sections. These sections exist between the text: "backtrace", and the following empty line.
My question is, how do I apply the flip flop operator to the local variable as if it were a file input?
Do you need to use the flip-flop operator? How about a regular expression?
#backtrace_sections = $log =~ /(^backtrace.*?)\n\n/gm;
I assume what you want is an equivalent of the construct
while (<>) {
if (m/backtrace/ .. m/^$/) {
# processing
}
}
I see two ways to do this off the top of my head:
Use the backtick operator in array context:
my #lines = qx{$your_command};
for (#lines) {
if (m/backtrace/ .. m/^$/) {
# process
}
}
Use open to open the file:
open my $fh, '-|', qq{$your_command} or die "Can't open command: $!";
while (<$fh>) {
if (m/backtrace/ .. m/^$/) {
# process
}
}
close $fh or die "close failed: $! $?";
Doing it this way has the nice effect that you don't have to read the entire output into memory.
Related
This post demonstrates how one can read from STDIN or from a file, without using the null filehandle (i.e., while(<>)). However, I'd like to know how can one address situations where input may come from files, STDIN, or both simultaneously.
For instance, the <> syntax can handle such a situation, as demonstrated by the following minimal example:
$ echo -e 'a\nb\nc' | \
while read x; do echo $x > ${x}".txt"; done; echo "d" | \
perl -e "while(<>) {print;}" {a,b,c}.txt -
a
b
c
d
How can I do this without using while(<>)?
I want to avoid using <> because I want to handle each file independently, rather than aggregating all input as a single stream of text. Moreover, I want to do this without testing for eof on every line of input.
If you want to handle each file independently of the others, you should loop over the arguments that have been given and open each file in turn:
for (#ARGV) {
open(my $fh, '<', $_) || die "cannot open $_";
while (<$fh>) {
... process the file here ...
}
}
# handle standard input
while (<STDIN>) {
...
}
Here is an idea based on Tim's that checks if STDIN has something to read (NON BLOCKING STDIN). This is useful if you don't really care about a user entering input manually from STDIN yet still want to be able to pipe and redirect data to the script.
File: script.pl
#!/usr/bin/env perl
use IO::Select;
$s = IO::Select->new();
$s->add(\*STDIN);
if ($s->can_read(0)) { push #ARGV, "/dev/stdin"; }
for (#ARGV) {
open(IN, "<$_") || die "** Error opening \"$_\": $!\n";
while (<IN>) {
print $_
}
}
$> echo "hello world" | script.pl
hello world
$> script.pl < <(echo "hello world")
hello world
$> script.pl <(echo "hello world")
hello world
$> script.pl <<< "hello world"
hello world
$> script.pl
$>
This was already answered by the Answer to which the question links.
#ARGS = '-' if !#ARGV;
for my $qfn (#ARGV) {
open($fh, $qfn);
while (<$fh>) {
...
}
}
I am new to Perl and trying to write a code to keep executing an action until the match is found and else give an error.
I am trying to execute a command ps -ef and check if it has got any process running in the name of "box", if there is no process named "box" found, I want to repeat ps -ef command execution until it gets the "box" process and then proceed to next action.
#!/usr/bin/perl -w
open (FH, "ps -ef |") or die "Cannot run the command:$!\n";
$line = "box";
while (<FH>) {
if (/$line/i) { next; }
else {
print ("ps -ef |") or die "Cannot run the command:$!\n");
}
}
close (FH);
You need to use an infinite loop and an exit-condition. Your condition is that the ps -ef command contains the word box. There is no need to open a pipe to that command explicitly, you can just run it as a system call with the qx operator (same as backticks).
use strict;
use warnings;
my $ps;
PS: while (1) {
$ps = qx/ps -ef/;
last PS if $ps =~ m/box/i;
print '.'; # do something in every run
}
print $ps;
As this has come up in the comments as well as in in AdrianHHH's answer: it might make sense to sleep after every run to make sure you don't hog the CPU. Depending on the nature of the process you are looking for, either the sleep builtin or usleep from Time::HiRes might be appropriate. The latter let's your program rest for milliseconds, while the builtin only works with full seconds. These might be too long if the target box process is very quick.
Explanation of your code:
Note that you have some issues in your implementation. I'll explain what your code does. This is taken from the question, comments are mine.
#!/usr/bin/perl -w
# open a filehandle to the ps command
open (FH, "ps -ef |") or die "Cannot run the command:$!\n";
$line = "box";
# read the output of one run line by line, for each line execute
# the block
while (<FH>) {
# if there is 'box' case-insensitive, skip the line
if (/$line/i) { next; }
else {
# else output (not run!) the command
print ("ps -ef |") or die "Cannot run the command:$!\n");
}
}
close (FH);
After it went through all the lines of the output of your command once it will stop.
I would recommend using pgrep(1) instead of ps because it lets you do a more granular search. With ps -ef, you potentially have to deal with cases like:
boxford 6254 6211 0 08:23 pts/1 00:00:00 /home/boxford/box --bounding-box=123
It's hard to tell if you're matching a process being run by a user with box in their username, a process that has box somewhere in its path, a process named box, or a process with box somewhere in its argument list.
pgrep, on the other hand, lets you match against just the process name or the full path, a specific user or users, and more. The following prints a message when a process named box appears (this looks for an exact match, so it will not match processes named dropbox, for example):
use strict;
use warnings;
use 5.010;
use String::ShellQuote qw(shell_quote);
sub is_running {
my ($proc) = #_;
my $cmd = 'pgrep -x ' . shell_quote($proc) . ' >/dev/null 2>&1';
system($cmd);
if ($? == -1) {
die "failed to execute pgrep: $!";
}
elsif ($? & 127) {
die "pgrep died with signal ", $? & 127;
}
else {
my $status = $? >> 8;
die "pgrep exited with error: exit status $status" if $status > 1;
return $status == 0;
}
}
my $proc = 'box';
until ( is_running($proc) ) {
sleep 1;
}
say "Process '$proc' is running";
Note that pgrep doesn't have a case-insensitive flag, probably because process names in *nix are almost always lowercase. If you really need to do a case-insensitive match, you can pass [Bb][Oo][Xx] to the is_running function.
The ps command outputs the current list of processes, then it completes. The code in the question reads that output. Suppose that the first ps command that is executed does not contain the wanted line, then there is nothing in the code in the question to run the ps command again.
The next statement in the question makes the script move on to the next line in the output from ps, not to rerun the command. The else print ... after the next will probably be executed for the first line of the output from ps. The outcome is that the print is run for each line in the ps output that does not have the wanted text and that the next command has no significant effect. In the code print ... or die "..." the or die "..." part is not very useful, the print is unlikely to fail and even if it did the die message would be wrong.
Perhaps you should write some code in the following style. Here the ps is run repeatedly until the wanted text is found. Note the sleep call, without that the script will keep running without pause, possibly preventing real work or at least slowing it down.
# This code is not tested.
use strict;
use warnings;
my $found_wanted_line = 0; # Boolean, set to false
my $line = "box";
while ( ! $found_wanted_line ) {
open (my $FH, "ps -ef |") or die "Cannot run the command:$!\n";
while (<$FH>) {
if (/$line/i) {
$found_wanted_line = 1; # Boolean, set to true
last;
}
}
close ($FH);
if ( ! $found_wanted_line )
sleep 2; # Pause for 2 seconds, to prevent this script hogging the CPU.
}
}
I need to run a shell command with system() in Perl. For example,
system('ls')
The system call will print to STDOUT, but I want to capture the output into a variable so that I can do future processing with my Perl code.
That's what backticks are for. From perldoc perlfaq8:
Why can't I get the output of a command with system()?
You're confusing the purpose of system() and backticks (``). system()
runs a command and returns exit status information (as a 16 bit value:
the low 7 bits are the signal the process died from, if any, and the
high 8 bits are the actual exit value). Backticks (``) run a command
and return what it sent to STDOUT.
my $exit_status = system("mail-users");
my $output_string = `ls`;
See perldoc perlop for more details.
IPC::Run is my favourite module for this kind of task. Very powerful and flexible, and also trivially simple for small cases.
use IPC::Run 'run';
run [ "command", "arguments", "here" ], ">", \my $stdout;
# Now $stdout contains output
Simply use similar to the Bash example:
$variable=`some_command some args`;
That's all. Notice, you will not see any printings to STDOUT on the output because this is redirected to a variable.
This example is unusable for a command that interact with the user, except when you have prepared answers. For that, you can use something like this using a stack of shell commands:
$variable=`cat answers.txt|some_command some args`;
Inside the answers.txt file you should prepare all answers for some_command to work properly.
I know this isn't the best way for programming :) But this is the simplest way how to achieve the goal, specially for Bash programmers.
Of course, if the output is bigger (ls with subdirectory), you shouldn't get all output at once. Read the command by the same way as you read a regular file:
open CMD,'-|','your_command some args' or die $#;
my $line;
while (defined($line=<CMD>)) {
print $line; # Or push #table,$line or do whatever what you want processing line by line
}
close CMD;
An additional extended solution for processing a long command output without extra Bash calling:
my #CommandCall=qw(find / -type d); # Some example single command
my $commandSTDOUT; # File handler
my $pid=open($commandSTDOUT),'-|'); # There will be an implicit fork!
if ($pid) {
#parent side
my $singleLine;
while(defined($singleline=<$commandSTDOUT>)) {
chomp $line; # Typically we don't need EOL
do_some_processing_with($line);
};
close $commandSTDOUT; # In this place $? will be set for capture
$exitcode=$? >> 8;
do_something_with_exit_code($exitcode);
} else {
# Child side, there you really calls a command
open STDERR, '>>&', 'STDOUT'; # Redirect stderr to stdout if needed. It works only for child - remember about fork
exec(#CommandCall); # At this point the child code is overloaded by an external command with parameters
die "Cannot call #CommandCall"; # Error procedure if the call will fail
}
If you use a procedure like that, you will capture all procedure output, and you can do everything processing line by line. Good luck :)
I wanted to run system() instead of backticks because I wanted to see the output of rsync --progress. However, I also wanted to capture the output in case something goes wrong depending on the return value. (This is for a backup script). This is what I am using now:
use File::Temp qw(tempfile);
use Term::ANSIColor qw(colored colorstrip);
sub mysystem {
my $cmd = shift; # "rsync -avz --progress -h $fullfile $copyfile";
my ($fh, $filename) = tempfile();
# http://stackoverflow.com/a/6872163/2923406
# I want to have rsync progress output on the terminal AND capture it in case of error.
# Need to use pipefail because 'tee' would be the last cmd otherwise and hence $? would be wrong.
my #cmd = ("bash", "-c", "set -o pipefail && $cmd 2>&1 | tee $filename");
my $ret = system(#cmd);
my $outerr = join('', <$fh>);
if ($ret != 0) {
logit(colored("ERROR: Could not execute command: $cmd", "red"));
logit(colored("ERROR: stdout+stderr = $outerr", "red"));
logit(colored("ERROR: \$? = $?, \$! = $!", "red"));
}
close $fh;
unlink($filename);
return $ret;
}
# And logit() is something like:
sub logit {
my $s = shift;
my ($logsec, $logmin, $loghour, $logmday, $logmon, $logyear, $logwday, $logyday, $logisdst) = localtime(time);
$logyear += 1900;
my $logtimestamp = sprintf("%4d-%02d-%02d %02d:%02d:%02d", $logyear, $logmon+1, $logmday, $loghour, $logmin, $logsec);
my $msg = "$logtimestamp $s\n";
print $msg;
open LOG, ">>$LOGFILE";
print LOG colorstrip($msg);
close LOG;
}
I'm attempting to pass perl variables into a system command and then capture the output for later usage, here's my current code:
my $updatedCmd = "|svn diff --summarize $svnOldFull $svnNewFull";
my $updatedUrls = '';
open UPDATES, $updatedCmd or die "Can't get updates";
while(<UPDATES>) {
print $_;
}
print "THIS_SHOULD_OUTPUT_AT_THE_END\n";
The problem with this is that I get the output:
THIS_SHOULD_OUTPUT_AT_THE_END
A /test
A /test2
A /deployment.txt
I would like to be able to capture all of the command output before allowing my perl script to go any further however.
More modern way to do this is the following:
my #cmd = qw(svn diff --summarize), $svnOldFull, $svnNewFull;
open my $pipe, '-|', #cmd or die "oops: $!";
while (<$pipe>) { ... }
Advantages
no globals
open mode separated from file/command
command as array, so there is no need in shell quoting
You placed the pipe on the wrong end of your command. Try this:
my $updatedCmd = "svn diff --summarize $svnOldFull $svnNewFull|";
I have the following code, the only problem is that when the code gets to the nested while loop it skips it, I'm assuming the condition is not being met, but can anyone see something I amy have done wrong? I have verified that all the flags that I give to the script are correct and that the job_name is what I think it should be.
open $alOut,
"/home/usr/bin/test.pl -j EW-% -j RA-% -l 0 | grep `date \"+%m/%d/%Y\"` | sort -k 3,3|";
while (<$alOut>) {
chomp;
my ($job_name, $date, $start_time, $end_time, $duration,
$state, $return, $expected_end_time) = split(/\s+/, $_);
# Go to next iteration if jobname is EW-INTERNAL-AUTOSYS,
# EW-INTERNAL-DB-LONGQUERY-ALERT, EW-INTERNAL-DB-LONGQUERY-ALERT,
# EW-CIIM-ADJ-TRIGGER, or EW-S140-ADJ-TRIGGER
if (($job_name eq "EW-INTERNAL-AUTOSYS") ||
($job_name eq "EW-INTERNAL-DB-LONGQUERY-ALERT") ||
($job_name eq "EW-INTERNAL-SYSUP") ||
($job_name eq "EW-CIIM-ADJ-TRIGGER") ||
($job_name eq "EW-S140-ADJ-TRIGGER"))
{
next;
}
#Expected Start Time
open $alOut2,
"/home/usr/bin/test.pl -j $job_name -q -l 0 | grep -E `condition:|start_times:`";
while (<$alOut2>) { .... }
}
You should check for errors from open:
open $fh, ... or die "Can't open: $!";
And in this grep:
grep `condition:|start_times:`
you probably want regular single quotes ('), not backticks, the shell is going to try to run a command called condition:. And I think you are missing a final | in that command.
You should always check the value returned by open:
open "...whatever..." or die "Can't open: $!";
That will probably tell you all you need to know, but offhand, I can see two problems:
The second open isn't terminated by a | character.
The backticks after the grep should be apostrophes.