Manipulation of data with BASH - bash

Question

I have a file full of lines like the following:
8408292236 48.04 46n20.13 12e43.22 1.00 3.1 MCSTI 0.4897 108 0.10 0.10 20 41 84EV01978
The first two digits in the first column represent the year and I need to substitute them with the full year while retaining the full line. I tried various method with awk and sed but couldn't get them working.
My latest attempt is the following:
while read line
a=20
b=19
do
awk '{ if ("$1 | cut -c1-2" == "0"); then {print $a$1}; }' > test.txt
done < catalog.txt
The final output should be:
198408292236 48.04 46n20.13 12e43.22 1.00 3.1 MCSTI 0.4897 108 0.10 0.10 20 41 84EV01978
Any ideas on how I can do this? Any help would be greatly appreciated.

Answer 1

You have a conceptional problem. How would you know whether 15 refers to 2015 or 1915. Otherwise it's quite easy:
#!/bin/bash
for num in 8408292236 8508292236 0408292236 1508292236
do
prefix=${num:0:2} # get first two digits of line
if [ $prefix -ge 20 ]; then # assuming that 0-20 refers to the 2000s
echo "19$num"
else
echo "20$num"
fi
done

Answer 2

This will prefix 19 if the first field starts with 16 or more, and will prefix 20 otherwise. I think this is what you need.
awk ' { if ($1 > 1600000000 ) print "19" $0 ; else print "20" $0 ; }' catalog.txt

Answer 3

A solution using just bash:
while read A; do
PREFIX=20
if [ ${A:0:2} -gt 15 ] ; then
PREFIX=19
fi
echo "${PREFIX}${A}"
done

Answer 4

sed -e 's/^[0-3]/20\0/' -e 's/^[4-9]/19\0/'
This will append 19 to each line starting with 3 to 9 or 20 to each line starting with 0 to 2, so we consider 30 - 99 to correspond to 1900, and 00-29 to correspond to 2000.
Adapt to your need.

Answer 5

Use awk ternary operator.
$ cat catalog.txt
8408292236 48.04 46n20.13 12e43.22 1.00 3.1 MCSTI 0.4897 108 0.10 0.10 20 41 84EV01978
0408292236 48.04 46n20.13 12e43.22 1.00 3.1 MCSTI 0.4897 108 0.10 0.10 20 41 84EV01978
$ awk '$1=substr($1,1,2)<15 ? "20"$1 : "19"$1' catalog.txt
198408292236 48.04 46n20.13 12e43.22 1.00 3.1 MCSTI 0.4897 108 0.10 0.10 20 41 84EV01978
200408292236 48.04 46n20.13 12e43.22 1.00 3.1 MCSTI 0.4897 108 0.10 0.10 20 41 84EV01978
Explanation
Let’s use the ternary operator.
expr ? action1 : action2
Its pretty straight forward: if expris true then action1 is performed/evaluated , if not action2.
Field one must be prefixed with 19 or 20 depending of it's two first chars value substr($1,1,2).
NOTE: This only works if your data does not contains years bellow 1915.
At this point, we just need to change the first field $1 to our needs: $1=substr($1,1,2)<15 ? "20"$1 : "19"$1
Check: http://klashxx.github.io/ternary-operator/

Answer 6

Simply in bash:
while read i; do echo "$((${i:0:2}<20?20:19))$i"; done <file.txt
shorter in perl:
perl -pe'print substr($_,0,2)<20?20:19' file.txt
even shorter in sed:
sed 's/^[01]/20&/;t;s/^/19/' file.txt