The following file access commands are UNIX commands, not specific shell commands.
| Command | Remakr |
|---|---|
| find | Finds the location of a file |
| sort | Reads a file and sort the output |
| hear or tail | Looks at just the start or end of a file |
The find Command
The find command allows you to search for files and directories and to execute commands on those files. The syntax of the find command has three general argument sections. The paths section is a list of pathnames (directories) to search. The search_criteria section is a list of options that are considered to be a Boolean (true or false) expression. Each option (condition) is tested in turn and if the result is true, the indicated action is taken.
A few of the possible search criteria are:
- -name – If the file name matches
- -user – If the file belongs to a user (login name)
- -atime – If the file was accessed the specified number of days ago
- -mtime – If the file was last modified the specified number of days ago
- -size – If the file is the specific block size
A few of the possible actions are:
- -print – Displays the path name of the file
- -exec – Executes the command
- -ok – Executes the command only after receiving a y from stdin
Examples of Using the find Command
You do not need to know the entire name of the file to find it. For example, log files tend to grow rather rapidly. As a system administrator, you might want to watch the size of log files. To search for the administrative log files (files in the /var/log directory), use the following command:
# find /var/log -name "*.log" -print /var/log/audit/audit.log /var/log/tuned/tuned.log /var/log/cloud-init.log /var/log/pm-powersave.log /var/log/awslogs-agent-setup.log /var/log/awslogs.log /var/log/boot.log /var/log/wpa_supplicant.log /var/log/amazon/ssm/amazon-ssm-agent.log /var/log/amazon/ssm/errors.log /var/log/amazon/ssm/hibernate.log /var/log/dpkg.log /var/log/yum.log /var/log/auth.log
As part of a file system clean-up, you might want to search for core files and delete them. The following two commands find any file named core. The first command executes the rm command without operator input. The second command prints the rm command and requires operator input.
$ find / -name core -exec rm -f {} \;
$ find / -name core -ok rm -f {} \; To find files that are larger than 1000 blocks, use the following command:
$ find / -size +1000 -print
The sort Command
A file, such as the password file, is frequently built by adding new users to the end of the file. The file is not in any particular order; however, when you are looking for something or someone in the file, it would be helpful if the file was sorted in some order. The sort command provides a way to sort the file.
Some of the more commonly used sort options are:
- -r – Sorts in reverse order (z to a, instead of a to z)
- -n – Sorts the fields numerically, instead of as just American Standard Code for Information Interchange (ASCII) strings
- -t [ch] – Sets the field separator character
- + num – Sets the field number from which to begin sorting (fields are numbered from 0 [zero])
- – num – Sets the field number to stop sorting before (this is the first field that is not considered for sorting)
- -b – Ignores leading blanks (they are normally considered to be part of the fields specified during keyed sorts)
- -r – Sorts in reverse order (z to a, instead of a to z)
- -o – file Sets the file to be used to hold the output of the sort (which might be the same file that contains the original input)
# cat /etc/passwd root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin sync:x:5:0:sync:/sbin:/bin/sync shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown halt:x:7:0:halt:/sbin:/sbin/halt mail:x:8:12:mail:/var/spool/mail:/sbin/nologin operator:x:11:0:operator:/root:/sbin/nologin games:x:12:100:games:/usr/games:/sbin/nologin ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin nobody:x:99:99:Nobody:/:/sbin/nologin dbus:x:81:81:System message bus:/:/sbin/nologin polkitd:x:999:998:User for polkitd:/:/sbin/nologin ...
To sort the file by the login name, use the following command:
# sort /etc/passwd adm:x:3:4:adm:/var/adm:/sbin/nologin apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin avahi-autoipd:x:170:170:Avahi IPv4LL Stack:/var/lib/avahi-autoipd:/sbin/nologin avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin bin:x:1:1:bin:/bin:/sbin/nologin chrony:x:998:996::/var/lib/chrony:/sbin/nologin cloud_user:x:1002:1003::/home/cloud_user:/bin/bash colord:x:997:995:User for colord:/var/lib/colord:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin dbus:x:81:81:System message bus:/:/sbin/nologin ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin games:x:12:100:games:/usr/games:/sbin/nologin gdm:x:42:42::/var/lib/gdm:/sbin/nologin geoclue:x:994:990:User for geoclue:/var/lib/geoclue:/sbin/nologin halt:x:7:0:halt:/sbin:/sbin/halt ...
To sort the file by the 5th field (the comment), where fields are separated by the colon, use the following command:
# sort -t: -k5 /etc/passwd tss:x:59:59:Account used by the trousers package to sandbox the tcsd daemon:/dev/null:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin nfsnobody:x:65534:65534:Anonymous NFS User:/var/lib/nfs:/sbin/nologin apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin avahi-autoipd:x:170:170:Avahi IPv4LL Stack:/var/lib/avahi-autoipd:/sbin/nologin avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin games:x:12:100:games:/usr/games:/sbin/nologin halt:x:7:0:halt:/sbin:/sbin/halt ...
You can put the output of a sort into a file. You can even output the sort into the original file; for example:
# cat names Big Ape 415 Roger Rabbit 408 Jessica Rabbit 510 Easter Rabbit 408 Doctor Doom 415 Easter Rabbit 408 Peter Wolf 510 Roger Rabbit 408 Peter Rabbit 510
# sort names -o names
Verify the file again:
# cat names Big Ape 415 Doctor Doom 415 Easter Rabbit 408 Easter Rabbit 408 Jessica Rabbit 510 Peter Rabbit 510 Peter Wolf 510 Roger Rabbit 408 Roger Rabbit 408
If you have multiple files, already sorted, that you want to merge into a single file, use the following command:
# sort file1 file2 file3 -o file4
Merging files might give you duplicate entries. To output only the unique lines of the file, use the following command:
# sort -u names Big Ape 415 Doctor Doom 415 Easter Rabbit 408 Jessica Rabbit 510 Peter Rabbit 510 Peter Wolf 510 Roger Rabbit 408
Reading Part of a File
Frequently, you do not want to review an entire file. You might want to browse the beginning of the file to determine if it is the correct one or look at the end of a file to review what was last entered in the file.
The head Command
To review the start of a file, use the head command:
# head -5 /etc/passwd root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
The tail Command
When reviewing log files, you are probably interested in only the last few entries of that file. You can use the tail command to look at the end of the file.
# tail -5 /etc/passwd systemd-network:x:995:991:systemd Network Management:/:/sbin/nologin geoclue:x:994:990:User for geoclue:/var/lib/geoclue:/sbin/nologin cloud_user:x:1002:1003::/home/cloud_user:/bin/bash ssm-user:x:1003:1004::/home/ssm-user:/bin/bash apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin