Here is a original awk file ,i want to format it.

input content----original awk file named test.txt

awk 'BEGIN {maxlength = 0}\
     {\
           if (length($0) > maxlength) {\
                maxlength = length($0);\
                longest = $0;\
           }\
     }\
     END   {print longest}' somefile

expected output----well-formatted awk file

awk 'BEGIN {maxlength = 0}                      \
     {                                          \
           if (length($0) > maxlength) {        \
                maxlength = length($0);         \
                longest = $0;                   \
           }                                    \
     }                                          \
     END   {print longest}' somefile

step1:to get the longest line and chracters number

step1.awk

#! /usr/bin/awk
BEGIN {max =0 }
{
    if (length($0) > max) { max = length($0)}
}
END {print max}

awk -f step1.awk test.txt

Now the max length for all lines is 50.

step2 to put \ in the position 50+2=52.

step2.awk

#! /usr/bin/awk
{
if($0 ~ /\\$/){
    gsub(/\\$/,"",$0);
    printf("%-*s\\\n",n,$0);
    }
else{
    printf("%s\n",$0);
    }
}

awk -f step2.awk -v n=52 test.txt > well_formatted.txt

How to combine step1 and step2 into only one step,and combine step1.awk and step2.awk as one awk file?

Better version, where you can use sub() instead of gsub(), and to avoid testing the same regexp twice sub(/\\$/,""){ ... }

awk 'FNR==NR{
             if(length>max)max = length
             next
     }
     sub(/\\$/,""){
             printf "%-*s\\\n", max+2, $0
             next
     }1' test.txt test.txt

Explanation

awk 'FNR==NR{                             # Here we read file and will find,
                                          # max length of line in file
                                          # FNR==NR is true when awk reads first file

             if(length>max)max = length   # find max length
             next                         # stop processing go to next line
     }
     sub(/\\$/,""){                       # Here we read same file once again,
                                          # if substitution was made for the regex in record then

             printf "%-*s\\\n", max+2, $0 # printf with format string max+2
             next                         # go to next line
     }1                                   # 1 at the end does default operation print $0,
                                          # nothing but your else statement printf("%s\n",$0) in step2
     ' test.txt test.txt

You have not shown us, what's your input and expected output, with some assumption,

if your input looks like below

[email protected]:/tmp$ cat f
123      \
\
12345
123456   \
1234567  \
123456789
12345

You get output as follows

[email protected]:/tmp$ awk 'FNR==NR{ if(length>max)max = length; next}
sub(/\\$/,"",$0){ printf "%-*s\\\n",max+2,$0; next }1' f f
123         \
            \
12345
123456      \
1234567     \
123456789
12345

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