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Full Discussion: False positive grep?
Top Forums Shell Programming and Scripting False positive grep? Post 303045879 by Chubler_XL on Thursday 16th of April 2020 05:55:04 PM
Old 04-16-2020
I do remember you being quite concerned with performance in this SWARM stuff and I would have thought the bash =~ operator could be use in place of grep.

Code:
$ export NUM='[['
$ time bash -c 'echo "$NUM" | grep -q "^\[\[" && echo yes'
yes

real    0m0.200s
user    0m0.000s
sys     0m0.107s
$ time bash -c '[[ "$NUM" =~ ^\[\[ ]] && echo yes'
yes

real    0m0.099s
user    0m0.015s
sys     0m0.046s

Twice as fast on my system, but your mileage may vary
This User Gave Thanks to Chubler_XL For This Post:
 

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TIMES(P)						     POSIX Programmer's Manual							  TIMES(P)

NAME
times - write process times SYNOPSIS
times DESCRIPTION
The times utility shall write the accumulated user and system times for the shell and for all of its child processes, in the following POSIX locale format: "%dm%fs %dm%fs %dm%fs %dm%fs ", <shell user minutes>, <shell user seconds>, <shell system minutes>, <shell system seconds>, <children user minutes>, <children user seconds>, <children system minutes>, <children system seconds> The four pairs of times shall correspond to the members of the <sys/times.h> tms structure (defined in the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 13, Headers) as returned by times(): tms_utime, tms_stime, tms_cutime, and tms_cstime, respectively. OPTIONS
None. OPERANDS
None. STDIN
Not used. INPUT FILES
None. ENVIRONMENT VARIABLES
None. ASYNCHRONOUS EVENTS
Default. STDOUT
See the DESCRIPTION. STDERR
The standard error shall be used only for diagnostic messages. OUTPUT FILES
None. EXTENDED DESCRIPTION
None. EXIT STATUS
Zero. CONSEQUENCES OF ERRORS
Default. The following sections are informative. APPLICATION USAGE
None. EXAMPLES
$ times 0m0.43s 0m1.11s 8m44.18s 1m43.23s RATIONALE
The times special built-in from the Single UNIX Specification is now required for all conforming shells. FUTURE DIRECTIONS
None. SEE ALSO
Special Built-In Utilities COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 TIMES(P)
All times are GMT -4. The time now is 05:18 PM.
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