Zero-fill numbers to 2 digits with sed Input: 201103 1 /mnt/hdd/PUB/SOMETHING 201102 7 /mnt/hdd/PUB/SOMETH ING 201103 11 /mnt/hdd/PUB/SO METHING 201104 3 /mnt/hdd/PUB/SOMET HING 201106 1 /mnt/hdd/PUB/SOMETHI NG Desired output: 201103 01 /mnt/hdd/PUB/SOMETHING 201102 07 /mnt/hdd/PUB/SOMETH ING 201103 11 /mnt/hdd/PUB/SO METHING 201104 03 /mnt/hdd/PUB/SOMET HING 201106 01 /mnt/hdd/PUB/SOMETHI NG How can I add a `0` if there is only a single digit, e.g. `1` in the "day" part? I need this date format: YYYYMM DD.

$ sed 's/\<[0-9]\>/0&/' ./infile
201103 01 /mnt/hdd/PUB/SOMETHING
201102 07 /mnt/hdd/PUB/SOMETH ING
201103 11 /mnt/hdd/PUB/SO METHING
201104 03 /mnt/hdd/PUB/SOMET HING
201106 01 /mnt/hdd/PUB/SOMETHI NG