Using AWK or SED how can I remove any line where the first column's character count doesn't equal 13

Question

Using AWK or sed how can I remove any line where the timestamp (first column) is not equal to 13 numeric characters while ignoring the first line.

Before:

timestamp,pageNo,description
1451317591621,01,Home Page Request
14513,Home Page Request
1451317591623,03,Home Page Request
1451317,04,Home Page Request
1451317591625,05,Home Page Request

After:

timestamp,pageNo,description
1451317591621,01,Home Page Request
1451317591623,03,Home Page Request
1451317591625,05,Home Page Request

Answer 1

Using sed , pass if the line number is one or the first field consists of exactly thirteen digits; else, delete.

sed -r -e '1b' -e '/^[0-9]{13},/b' -e d file

Using Awk, similarly, print if line number is one or the first field is thirteen characters and all numbers.

awk -F , 'NR == 1 || (len($1) == 13 && $1 ~ /^[0-9]*$/)' file

Answer 2

Using awk (requires gawk 4+ or 3+ with --re-interval option)

awk -F, '$1~/^[0-9]{13}$/||NR==1' file

Using sed

sed '/^[0-9]\{13\},/p;1p;d' file

Answer 3

awk -F, 'NR==1 || (length($1) == 13 && $1+0 == $1)' file 

Answer 4

If Perl is an option:

perl -F, -ane 'print if $F[0] =~ /^[0-9]{13}$/ or $. == 1' file

These command-line options are used:

• -n loop around each line of the input file
• -a autosplit mode – split input lines into the @F array. Defaults to splitting on whitespace.
• -e execute the perl code
• -F autosplit modifier, in this case splits on ,

$. is the line number
@F is the array of words in each line, indexed starting with $F[0]

output:

timestamp,pageNo,description
1451317591621,01,Home Page Request
1451317591623,03,Home Page Request
1451317591625,05,Home Page Request