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Full Discussion: $(< file ) and $( cat file )
Top Forums Shell Programming and Scripting $(< file ) and $( cat file ) Post 303012357 by Yoda on Friday 2nd of February 2018 02:07:21 PM
Old 02-02-2018
$(< filename ) - shell opens the file. $( cat filename ) - cat opens the file.

Create a simple script:-
Code:
#!/bin/ksh -xv

var1=$( cat file )
var2=$( < file )

and run strace to understand the difference:-
Code:
strace ./script.ksh 2> strace.out

This User Gave Thanks to Yoda For This Post:
RudiC
 

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LEARN ABOUT MINIX

strace-log-merge

STRACE-LOG-MERGE(1)					      General Commands Manual					       STRACE-LOG-MERGE(1)

NAME

       strace-log-merge - merge strace -ff -tt output

SYNOPSIS

       strace-log-merge STRACE_LOG

       strace-log-merge --help

DESCRIPTION

       strace-log-merge  merges  the output of strace -ff -tt[t] command, prepending PID to each line and sorting the result using time stamp as a
       key.

OPTIONS

       --help Show program usage and exit.

       STRACE_LOG
	      Output file name prefix of files produced by a strace -ff -tt[t] command.

EXIT STATUS

       0      Success

       Non-zero
	      Error occurred: either no argument specified (in that case a usage is printed), or something went wrong  during  the  processing	of
	      STRACE_LOG.*  files.

USAGE EXAMPLE

       $ strace -o sleepy -ff -tt -e trace=execve,nanosleep 
	       sh -c 'sleep 0.1 & sleep 0.2 & sleep 0.3'
       $ strace-log-merge sleepy | fold -w 72 -s
       13475 21:13:52.040837 execve("/bin/sh", ["sh", "-c", "sleep 0.1 & sleep
       0.2 & sleep 0."...], 0x7ffde54b2450 /* 33 vars */) = 0
       13478 21:13:52.044050 execve("/bin/sleep", ["sleep", "0.3"],
       0x5631be4f87a8 /* 33 vars */) = 0
       13476 21:13:52.044269 execve("/bin/sleep", ["sleep", "0.1"],
       0x5631be4f87a8 /* 33 vars */) = 0
       13477 21:13:52.044389 execve("/bin/sleep", ["sleep", "0.2"],
       0x5631be4f87a8 /* 33 vars */) = 0
       13478 21:13:52.046207 nanosleep({tv_sec=0, tv_nsec=300000000}, NULL) = 0
       13476 21:13:52.046303 nanosleep({tv_sec=0, tv_nsec=100000000}, NULL) = 0
       13477 21:13:52.046318 nanosleep({tv_sec=0, tv_nsec=200000000}, NULL) = 0
       13476 21:13:52.146852 +++ exited with 0 +++
       13475 21:13:52.146942 --- SIGCHLD {si_signo=SIGCHLD,
       si_code=CLD_EXITED, si_pid=13476, si_uid=1000, si_status=0, si_utime=0,
       si_stime=0} ---
       13477 21:13:52.247782 +++ exited with 0 +++
       13475 21:13:52.247885 --- SIGCHLD {si_signo=SIGCHLD,
       si_code=CLD_EXITED, si_pid=13477, si_uid=1000, si_status=0, si_utime=0,
       si_stime=0} ---
       13478 21:13:52.347680 +++ exited with 0 +++
       13475 21:13:52.347786 --- SIGCHLD {si_signo=SIGCHLD,
       si_code=CLD_EXITED, si_pid=13478, si_uid=1000, si_status=0, si_utime=0,
       si_stime=0} ---
       13475 21:13:52.348069 +++ exited with 0 +++

NOTES

       strace-log-merge  does  not work well with strace logs generated by strace -tt invocation that pass midnight, as those lack the information
       required for the proper sorting.  Employing the -ttt option in the respective strace invocation should solve the problem.

BUGS

       strace-log-merge does not perform any checks whether the files specified are in the correct format and implies that only files from a  sin-
       gle strace session match STRACE_LOG.*  glob pattern.

HISTORY

       The initial version of strace-log-merge was written by Denys Vlasenko in 2012.

REPORTING BUGS

       Problems with strace-log-merge should be reported to the strace mailing list at <strace-devel@lists.sourceforge.net>.

SEE ALSO

       strace(1)

strace UNKNOWN							    2018-04-11						       STRACE-LOG-MERGE(1)
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