aw.sh : use awk as quick custom calculator on command line -- with easy syntax. / Linux bash script.

aw.sh

#!/usr/bin/env bash
#              bash 4.2.24(1)     Linux Ubuntu 12.04          Date : 2012-09-13
#
# _______________|  aw : use awk as quick custom calculator on command line.
#
#           Usage:  aw  'expression'  [decimal/sig:8]  [format:g]
#                   aw  bak           #  show log file of previous result.
#                 
#
#    User-defined:  r =   random number strictly between 0 and 1,
#                            never 0 nor 1, see rand().
#                   s =   stored full result from previous script call.
#                   pi, e.    
#                   mil, bil, tri; pc, bp, milli, macro, nano.
#                   [ Also add your favorite functions.          ]
#                   [ Recommended format choices are e, f, or g. ]
#
#        Examples:  % aw '(3+2)*r'         
#                   4.63147                #  random real between 0 and 5.
#                   % aw r 0 f
#                   1                      #  random integer, 0 or 1.
#                   % aw '10 * pc * 210'
#                   21.0000                #  10% of 210
#                   % aw 's/2'
#                   10.5000                #  take half of previous result.
#
#    Dependencies:  gawk (on Ubuntu 12.04 prefer installing "gawk" package
#                         since inferior mawk of 1996 is the default awk.)
#                   This script will use system's awk if gawk is unavailable.
#
#    Definitive REFERENCE by Arnold Robbins, "gawk: Effective AWK Programming",
#       http://www.gnu.org/software/gawk/manual/    (2011)
#
#    WARNING: Unassigned variables in awk are given value of 0.
#       Thus do not misspell variable names!!
#
#    Exponentiation: the character sequence ** is equivalent to ^.
#    exp() is available; and the constant e is defined in the script.
#    log() is the natural logarithm.
#    int() is integer truncation.
#    Functions: sqrt, sin, cos, and atan2 are also available in gawk.


#  CHANGE LOG  LATEST version available:   https://bitbucket.org/rsvp/gists/src
#  2012-09-13  Add variable for awkprg, in case gawk is unavailable.
#                 printf modified for portability.
#                 Replace both head and tail by sed for portability.
#                 Memorialize first argument on memf's third line.
#  2012-09-10  Add printf format as third argument.
#                 Shadow the full result into storage.
#  2012-09-09  First version using gawk 3.1.8 under Ubuntu 12.04, 
#                 script patterned on pye. gawk is 12% the size of Python.
#                 Fixed awk's seed for randomness problem.


#           _____ PREAMBLE_v2: settings, variables, and error handling.
#
LC_ALL=POSIX
#      locale means "ASCII, US English, no special rules, 
#      output per ISO and RFC standards." 
#      Esp. use ASCII encoding for glob and sorting characters. 
shopt -s   extglob
#     ^set extended glob for pattern matching.
shopt -s   failglob
#         ^failed pattern matching signals error.
set -e
#   ^errors checked: immediate exit if a command has non-zero status. 
set -u
#   ^unassigned variables shall be errors.
#    Example of default VARIABLE ASSIGNMENT:  arg1=${1:-'foo'}

ndec=${2:-'8'}
#         ^default number of significant or decimal places.
#          ndec=0 gives rounded integer result [unlike int()], but
#          see printf section below for important rounding caveats.
letter=${3:-'g'}
#           ^control printf format, e.g. e, f, g -- for
#            exponent, float, or mixture with max significant digits.


program=${0##*/}   #  similar to using basename
#  memf=$( mktemp /dev/shm/88_${program}_tmp.XXXXXXXXXX )
memf="/dev/shm/88_${program}_tmp"
#    ^intended to persist, to save last result.



cleanup () {
     #  Delete temporary files, then optionally exit given status.
     local status=${1:-'0'}
     #  rm -f $memf
     [ $status = '-1' ] ||  exit $status      #  thus -1 prevents exit.
} #--------------------------------------------------------------------
warn () {
     #  Message with basename to stderr.          Usage: warn "message"
     echo -e "\n !!  ${program}: $1 "  >&2
} #--------------------------------------------------------------------
die () {
     #  Exit with status of most recent command or custom status, after
     #  cleanup and warn.      Usage: command || die "message" [status]
     local status=${2:-"$?"}
     cleanup -1  &&   warn "$1"  &&  exit $status
} #--------------------------------------------------------------------
trap "die 'SIG disruption, but cleanup finished.' 114" 1 2 3 15
#    Cleanup after INTERRUPT: 1=SIGHUP, 2=SIGINT, 3=SIGQUIT, 15=SIGTERM
#
# _______________     ::  BEGIN  Script ::::::::::::::::::::::::::::::::::::::::

if  ( which gawk > /dev/null ) ; then
     awkprg='gawk'
else
     #  warn "gawk is not installed. Falling back on system's awk."  #-DEBUG
     awkprg='awk'
     #       Ubuntu 12.04 awk defaults to inferior mawk.
fi


#  Retrieve result from previous execution:
if [ -s $memf ] ; then
     stored="$( sed -n -e '2p' $memf )"
     #                    ^pick out the second printf from gawk output.
     if [ "$1" = 'bak' ] ; then
          cat $memf
          cleanup
     fi
else
     stored=0
     #      ^expected awk behavior.
fi


#-------------------------------------- awk at work...
{ $awkprg -f - <<EOHereDoc
BEGIN { 
s   = "$stored"
e   = 2.718281828459045
pi  = 3.141592653589793
mil = 1000000
bil = 1000000000
tri = 1000000000000
pc    = 0.01
milli = 0.001
bp    = 0.0001
macro = 0.000001
nano  = 0.000000001
srand( $(date '+%N') )   
#    ^To SEED the random generator,
#     awk by default uses time which does not change for  1 sec,
#     thus executions during that second gives the same output.
#     Our FIX is to use the nanoseconds portion of time
#     which looks like 877928409 -- nine digits.
#     Execution of aw one nanosecond apart generates, e.g. 
#        0.5656
#        0.1706
#        0.2621
#        0.2180
#        0.0804
#        0.7866
#     So it looks like the neighborhood problem is avoided.
}


     function pch (x, y) {
     #        percentage change
     return ( (y-x)/x )*100
     }


     #  There is no middle section { }
     #  because that is for evalating each record.
     #  Of course, we have no records here!


END { 
r = rand()
# ^ one-time convenient random number variable.
#   It costs virtually nothing in execution time.
evala = ( $1 )
#     ^ evaluated argument from command line.


printf "%.${ndec}${letter}\n", evala
#-X  printf "%1\$.${ndec}${letter}\n", evala  # OK on gawk, not on mawk.
#                   Floating-point with ndec number of decimal places.
#       ___ATTN___  printf does NOT round the decimal portion.
#       For ndec=0, we do not get integer truncation. 
#       Rounding is "unbiased," which means it doesn't always round 
#       a trailing '.5' up, contrary to naive expectations. 
#       In unbiased rounding, '.5' rounds to even, rather than always up, 
#       so 1.5 rounds to 2 but 4.5 rounds to 4. See
#       http://www.gnu.org/software/gawk/manual/html_node/Round-Function.html
#       which provide the usual rounding function.
#
#       CONVFMT's default value is "%.6g", which yields a value 
#       with at least six significant digits.


printf "%.15e\n", evala
#-X  printf "%1\$.15e\n", evala  # OK on gawk, not on mawk.
#       SECOND printf reports the FULL version for storage,
#       since the first printf may not have fully expressed 
#       the complete result due to user formatting.
}
EOHereDoc
}           >  $memf
#     Preserve TWO results into memory.            
#-------------------------------------- awk done.



#    Show just the requested format result on STDOUT,
#    i.e. the first printf within awk.
sed -n -e '1p' $memf
#-X  head -n1 $memf  #  replaced for portability.


echo "$1"  >>  $memf
#               memorialize first argument on memf's third line.



cleanup
# _______________ EOS ::  END of Script ::::::::::::::::::::::::::::::::::::::::

#  vim: set fileencoding=utf-8 ff=unix tw=78 ai syn=sh :