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Language: English ｜ Shell-Basics

Shell basics

The oc> shell is a Unix-flavoured command line - with pipes, redirection, background jobs, environment variables, aliases and a small scripting language. This page walks the real feature set.

Line editing

  • History: up/down arrows walk previous lines.
  • Editing within the line; Ctrl+U kills the line.
  • Input sources: PS/2 keyboard and COM1 serial feed the same queue - with -serial mon:stdio in QEMU you type over serial.

Command chaining and jobs

oc> dhcp && ping 10.0.2.2      (run ping only if dhcp succeeded)
oc> cat a.txt ; cat b.txt      (sequence regardless)
oc> health || dmesg            (second only if first failed)
oc> ping 10.0.2.2 &            (background job)
oc> g6_test &                  (long test in the background)

Pipes and redirection

oc> ls | grep log              (pipe stdout of ls into grep)
oc> cat /mnt/f.txt > /tmp/g.txt     (write stdout to a file)
oc> cat /mnt/f.txt >> /tmp/g.txt    (append)
oc> wget 10.0.2.2 < in.txt     (stdin from a file)

Wildcards

* and ? expand in the shell before the command runs:

oc> ls /mnt/*.txt
oc> cat /mnt/report?.txt

Environment variables

oc> export NAME=value          (set)
oc> echo $NAME                 (use - $VAR expands in the line)
oc> env                         (list all)

Environment storage limits: 32 variables, names up to 32 bytes, values up to 256 bytes (shell/shell.h).

Aliases

oc> alias ll ls -l
oc> ll
oc> unalias ll

Alias values may hold full pipelines - up to 512 bytes stored in full or refused (never silently truncated). 32 alias slots.

Current working directory

oc> cd /mnt
oc> pwd

Scripting

A script is a text file of command lines; feed it with the shell's script runner (see help -a for the exact command name in your build). The editor command gives you an in-guest full-screen text editor to write those scripts.

Command help

oc> help            (short list, one line per command)
oc> help -a         (all 233 commands, alphabetical, with descriptions)
oc> help -w         (the same commands grouped by the work package
                     that introduced them)

The complete indexed reference with one page per command is Command-Reference-EN.

The contract

Commands may be added across versions, never removed; names and overall behaviour of shipped commands are stable (see Contributing-EN). The command table capacity is 256 with 233 registered at present.

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