#!/bin/bash # redir2.sh if [ -z "$1" ] then Filename=names.data # Default, if no filename specified. else Filename=$1 fi #+ Filename=${1:-names.data} # can replace the above test (parameter substitution). count=0 echo while [ "$name" != Smith ] # Why is variable $name in quotes? do read name # Reads from $Filename, rather than stdin. echo $name let "count += 1" done <"$Filename" # Redirects stdin to file $Filename. # ^^^^^^^^^^^^ echo; echo "$count names read"; echo exit 0 # Note that in some older shell scripting languages, #+ the redirected loop would run as a subshell. # Therefore, $count would return 0, the initialized value outside the loop. # Bash and ksh avoid starting a subshell *whenever possible*, #+ so that this script, for example, runs correctly. # (Thanks to Heiner Steven for pointing this out.) # However . . . # Bash *can* sometimes start a subshell in a PIPED "while-read" loop, #+ as distinct from a REDIRECTED "while" loop. abc=hi echo -e "1\n2\n3" | while read l do abc="$l" echo $abc done echo $abc # Thanks, Bruno de Oliveira Schneider, for demonstrating this #+ with the above snippet of code. # And, thanks, Brian Onn, for correcting an annotation error.