Shell Programming and Scripting

#!/bin/bash

# Replace here whatever you want in 2nd field
replace=replaces

for file in file*; do
        awk -F, 'NR == 1 ; getline ; END{$2=replace;print}' OFS=\, replace=$replace $file >fl.tmp 
        cat fl.tmp >$file
done

rm fl.tmp

#!/bin/ksh
IAm=${0##*/}
if [ $# -lt 2 ]
then    printf "Usage: %s replacement_string file...\n" "$IAm" >&2
        exit 1
fi
rep="$1"
shift
for file in "$@"
do      printf "%s: Processing file %s\n" "$IAm" "$file"
        ed -s "$file" <<-EOF
                \$g/\([^,]*,\)[^,]*/s//\1$rep/
                w
                q
EOF
done

chmod +x tester

./tester "10-Aug" file[123]

ScriptName replacement_string field_number file...

#!/bin/ksh
IAm=${0##*/}
replacement="$1"
field="$2"
if [ $# -ge 3 ]
then    if [ ${#field} -eq 0 ] || [ "${field}" != "${field%*[^0-9]*}" ] ||
                [ $field -eq 0 ]
        then    printf "%s: invalid field# <%s>\n" "$IAm" "$field" >&2
                shift $#
        fi
fi
if [ $# -lt 3 ]
then    printf "Usage: %s replacement_string field# file...\n" "$IAm" >&2
        exit 1
fi
if [ "$2" -eq 1 ]
then    edCommandMiddle='[^,]*/'
else    BRE=''
        while [ $((field--)) -gt 1 ]
        do      BRE="${BRE}[^,]*,"
        done
        edCommandMiddle='\('"$BRE"'\)[^,]*/\1'
fi
shift 2
# printf "ed command will be: %s\n" '$'"s/^$edCommandMiddle$replacement/"
for file in "$@"
do      printf "%s: Processing file %s\n" "$IAm" "$file"
        ed -s "$file" <<-EOF
                \$s/^$edCommandMiddle$replacement/
                w
                q
EOF
done

./tester 'new text' 4 file[123]