シェアする
Advanced ls Command (Part 1) and Dotfiles - Images: Japanese
Hey there, everyone!
Let's continue with more on the ls command and an intro to dot files.
Quick recap first: 'ls' lists the contents of the current directory (the current working directory). It comes with a few options, so let's go through those.
Starting from the root directory /, a plain ls looks like this.
[root@localhost /]# ls bin dev home lib64 media opt root selinux sys usr boot etc lib lost+found mnt proc sbin srv tmp var
A quick scrolling list of directories and files.
Adding '-1' (the number one) makes it output one item per line. Note: '-2' and other numbers don't work — only '-1' does.
[root@localhost /]# ls -1 bin boot dev etc home lib lib64 lost+found media mnt opt proc root sbin selinux srv sys tmp usr var
Adding -R outputs the contents of subdirectories recursively — and then the contents of those subdirectories, and so on. Let's try it.
Say we're in '/root', and inside it we've created a 'test' directory, inside that another 'test' directory, and inside that yet another 'test' directory. A plain 'ls' shows this:
[root@localhost ~]# ls test
But with ls -R:
[root@localhost ~]# ls -R .: test ./test: test ./test/test: test ./test/test/test:
Every nested directory is listed. Useful when you want to understand the full structure of a directory tree.
As mentioned briefly in the previous article, the 'tree' command is a handy alternative to 'ls -R' for visualizing directory structure. Its output looks like this.
[root@localhost var/www]# tree
.
├── index.html
├── test
└── index.html
It shows the structure as an actual tree. The author tends to find tree more readable than ls -R for this purpose.
That said, 'tree' isn't installed by default on most systems. If you can't install it due to permission constraints, use 'ls -R' instead — it's a core command that's always available.
Next: '-F'. This appends a 'type indicator' after each filename or directory name in the output, indicating what kind of data each entry is.
| (nothing) | Regular file |
| * | Executable file |
| @ | Symbolic link |
| / | Directory |
Symbolic link is roughly equivalent to a shortcut in Windows.
Let's try 'ls -F' somewhere interesting. It's most informative in a directory full of executable files, so let's look at '/bin' — the home of core UNIX commands.
Here's a technique we haven't covered yet: 'ls' can take a path as its first argument. Instead of navigating to a directory with 'cd' and then running 'ls', you can pass the path directly to 'ls' and it'll list that directory's contents from wherever you are.
Let's use it. We'll move to the home directory first (for no particular reason — just to demonstrate).
[root@localhost bin]# cd [root@localhost ~]# pwd /root
From here, 'ls -F /bin' lists the contents of '/bin' with type indicators.
[root@localhost bin]# cd [root@localhost ~]# pwd /root [root@localhost ~]# ls -F /bin arch* fgrep@ mktemp* sort* awk@ find* more* stty* basename* findmnt* mount* su* bash* fusermount* mountpoint* sync* cat* gawk* mv* tar* chgrp* grep* netstat* taskset* chmod* gtar@ nice* touch* chown* gunzip* nisdomainname@ tracepath* cp* gzip* ping* tracepath6* cpio* hostname* ping6* true* cut* ipcalc* plymouth* ulockmgr_server* dash* iptables-xml@ ps* umount* date* iptables-xml-1.4.7@ pwd* uname* dd* kbd_mode* raw* unicode_start* df* kill* readlink* unicode_stop* dmesg* link* rm* unlink* dnsdomainname@ ln* rmdir* usleep* domainname@ loadkeys* rpm* vi* dumpkeys* logger* rvi@ view@ echo* login* rview@ ypdomainname@ egrep@ ls* sed* zcat* env* lsblk* setfont* ex@ mkdir* sh@ false* mknod* sleep*
The contents of '/bin' were listed from the home directory, and each entry has a type indicator at the end. Everything with a '*' is an executable, and entries with '@' are symbolic links.
That said — modern UNIX-based OSes already color-code 'ls' output by type, so type indicators via '-F' are rarely needed anymore. After spending so much time on it, the honest assessment is: you can probably ignore '-F'. The path argument for 'ls', on the other hand, is worth remembering.
'ls' can take multiple path arguments at once. When you do, it lists each one in turn. Here's an example with '/bin', '/etc', and '/var'.
[root@localhost ~]# ls /bin /etc /var /bin: arch echo kill ping6 tar awk egrep link plymouth taskset basename env ln ps touch bash ex loadkeys pwd tracepath cat false logger raw tracepath6 chgrp fgrep login readlink true chmod find ls rm ulockmgr_server chown findmnt lsblk rmdir umount cp fusermount mkdir rpm uname cpio gawk mknod rvi unicode_start cut grep mktemp rview unicode_stop dash gtar more sed unlink date gunzip mount setfont usleep dd gzip mountpoint sh vi df hostname mv sleep view dmesg ipcalc netstat sort ypdomainname dnsdomainname iptables-xml nice stty zcat domainname iptables-xml-1.4.7 nisdomainname su dumpkeys kbd_mode ping sync /etc: DIR_COLORS filesystems modprobe.d rpc DIR_COLORS.256color fstab motd rpm DIR_COLORS.lightbgcolor gai.conf mtab rsyslog.conf NetworkManager gcrypt multipath rsyslog.d X11 gnupg my.cnf rwtab adjtime group networks rwtab.d aliases group- nsswitch.conf sasl2 aliases.db grub.conf openldap securetty alternatives gshadow opt security anacrontab gshadow- pam.d selinux audisp host.conf passwd services audit hosts passwd- sestatus.conf bash_completion.d hosts.allow pkcs11 shadow bashrc hosts.deny pki shadow- blkid init plymouth shells centos-release init.conf pm skel chkconfig.d init.d popt.d ssh cron.d inittab postfix ssl cron.daily inputrc ppp statetab cron.deny iproute2 prelink.conf.d statetab.d cron.hourly iscsi printcap sudo-ldap.conf cron.monthly issue profile sudo.conf cron.weekly issue.net profile.d sudoers crontab krb5.conf protocols sudoers.d crypttab ld.so.cache rc sysconfig csh.cshrc ld.so.conf rc.d sysctl.conf csh.login ld.so.conf.d rc.local sysctl.d dbus-1 libaudit.conf rc.sysinit system-release default libuser.conf rc0.d system-release-cpe depmod.d localtime rc1.d terminfo dhcp login.defs rc2.d udev dracut.conf logrotate.conf rc3.d virc dracut.conf.d logrotate.d rc4.d xdg environment lvm rc5.d xinetd.d ethers magic rc6.d yum exports makedev.d redhat-release yum.conf favicon.png mke2fs.conf resolv.conf yum.repos.d /var: cache empty lib lock mail opt run tmp db games local log nis preserve spool yp
Pretty handy — give it a try.
Now let's look at '-a'. This is a high-frequency option. It makes 'ls' also show 'dot files'.
"What's a dot file?" — exactly what it sounds like: a file whose name starts with '.' (a dot). In UNIX-based OSes, files that shouldn't be casually touched — configuration files, for example — are conventionally named with a leading dot, which makes them hidden. So "dot file = hidden file" in UNIX terms.
Let's try it. Here's the output of ls -a at the root directory.
[root@localhost /]# ls -a . bin etc lib64 mnt root srv usr .. boot home lost+found opt sbin sys var .autofsck dev lib media proc selinux tmp
And here's 'ls' without '-a'.
[root@localhost /]# ls bin dev home lib64 media opt root selinux sys usr boot etc lib lost+found mnt proc sbin srv tmp var
Comparing the two: '.', '..', and '.autofsck' appear in the '-a' output but not without it.
'.autofsck' is the dot file here. The '.' and '..' entries are the same ones from the 'cd' article — '.' is the current directory, '..' is the parent directory.
"But the root directory is the very top — why does 'ls -a' at root show '..' for a parent that doesn't exist?" — that's a fair observation. The author has wondered about it too and looked into it before, but never found a clear answer. Just treat it as: "at the root directory, '..' also points to the root directory itself." Not something to worry about.
On the topic of '.autofsck' specifically: it's a file that UNIX-based OSes generate when the OS starts up and delete when the OS shuts down normally. On the next boot, if '.autofsck' already exists, the OS knows the previous shutdown wasn't clean. Side note — not something you need to memorize.
There's also a '-A' option (uppercase A). It behaves like '-a' but excludes the '.' and '..' entries from the output. If those two get in the way, '-A' is an option. In practice, '.' and '..' are rarely in the way, so '-a' is usually all you need.
By the way — a casual internal note: '-A' exists, but you'll almost never need it. Just remember '-a'.
Alright, that got a little long. Let's stop here and pick up with more ls content in the next article. See you there!
This article was written by Sakurama.
Author's beloved small mammal |
桜舞 春人 Sakurama HarutoA Tokyo-based programmer who has been creating various content since the ISDN era, with a bit of concern about his hair. A true long sleeper who generally feels unwell without at least 10 hours of sleep. His dream is to live a life where he can sleep as much as he wants. Loves games, sports, and music. Please share some hair with him. |
If you find any errors or copyright issues, please contact us.
