The column Command in Linux: Format Output in Columns, CSV, and JSON

The column command in Linux can really save a developer a lot of time. It allows you to format a file or command output into columns, CSV (comma-separated) or JSON.

This really saves a lot of time in data transformation.

For example, see the /etc/passwd file which contains the system users, with fields separated by colons:

$ cat /etc/passwdroot:x:0:0:root:/root:/bin/bashdaemon:x:1:1:daemon:/usr/sbin:/bin/falsebin:x:2:2:bin:/bin:/bin/falsesys:x:3:3:sys:/dev:/bin/falsesync:x:4:65534:sync:/bin:/bin/syncgames:x:5:60:games:/usr/games:/bin/falseman:x:6:12:man:/var/cache/man:/bin/false

The column command can be used to read the contents of this file, and separate it into columns:

$ column /etc/passwd -s : -troot     x  0  0    root    /root           /bin/bashdaemon   x  1  1    daemon  /usr/sbin       /bin/falsebin      x  2  2    bin     /bin            /bin/falsesys      x  3  3    sys     /dev            /bin/falsesync     x  4  655  sync    /bin            /bin/syncgames    x  5  60   games   /usr/games      /bin/falseman      x  6  12   man     /var/cache/man  /bin/false

The column command can also be used to view a Comma-Separated Values CSV file:

$ cat contatos.csv | column -t -s,NOME          TEL             EMAILUira Ribeiro  (31) 3069-8315  [email protected]

This can be useful for viewing this type of file without needing to have Excel or similar software.

In some distributions the column command allows you to export data in JSON format, using the "-J" option, followed by the column names:

$ cat /etc/passwd | column -t -s : -J --table-columns LOGIN,PASSWORD,UID,GUID,NOME,HOME,SHELL{   "table": [      {"login": "root", "password": "x", "uid": "0", "guid": "0", "nome": "root", "home": "/root", "shell": "/bin/bash"},      {"login": "bin", "password": "x", "uid": "1", "guid": "1", "nome": "bin", "home": "/bin", "shell": "/sbin/nologin"},      {"login": "daemon", "password": "x", "uid": "2", "guid": "2", "nome": "daemon", "home": "/sbin", "shell": "/sbin/nologin"},      {"login": "adm", "password": "x", "uid": "3", "guid": "4", "nome": "adm", "home": "/var/adm", "shell": "/sbin/nologin"},      {"login": "lp", "password": "x", "uid": "4", "guid": "7", "nome": "lp", "home": "/var/spool/lpd", "shell": "/sbin/nologin"},      {"login": "sync", "password": "x", "uid": "5", "guid": "0", "nome": "sync", "home": "/sbin", "shell": "/bin/sync"},      {"login": "shutdown", "password": "x", "uid": "6", "guid": "0", "nome": "shutdown", "home": "/sbin", "shell": "/sbin/shutdown"},      {"login": "halt", "password": "x", "uid": "7", "guid": "0", "nome": "halt", "home": "/sbin", "shell": "/sbin/halt"},      {"login": "mail", "password": "x", "uid": "8", "guid": "12", "nome": "mail", "home": "/var/spool/mail", "shell": "/sbin/nologin"},   ]}

This command can be used together with any system command, to generate JSON files.

See for example how easy it is to generate a list of files from a directory in JSON:

$ ls -1 |  column -t -J --table-columns ARQUIVO --table-name ARQUIVOS{   "ARQUIVOS": [      {"arquivo": "agradecimento.html"},      {"arquivo": "agradecimentos"},      {"arquivo": "amazon.php"},      {"arquivo": "backup.sh"},      {"arquivo": "certbot-auto"},      {"arquivo": "certificado"},      ]}

In this example, the output of the ls command, with the -1 option that lists only files one per line was transformed by the column command into a JSON file with a column called ARQUIVO, in the ARQUIVOS table.

Learn much more about Linux in our online course. You can enroll here. If you already have an account, or want to create one, just log in or create your user here.

Did you like it? Share