LED

Table of Contents

• Use example
• Installation
  • Non-standard libreadline location
• Usage
  • Key commands
  • Addressing

led is a line editor based around the GNU Readline library. Basically, it is an ed clone with Readline usability.

The main use case is when you want to quickly open and make a small change to a file without opening a full-screen editor. You can quickly jump to a certain line number or pattern and make a change without leaving your shell/terminal!

Use example

Inside led, use h for help.

Basic use:

# Start led to edit a file:
$ led myfile.txt
new file: myfile.txt
: a
   1> hello
: wq
backup: current file does not yet exist...
wrote:  myfile.txt

# Show the file using cat
$ cat myfile.txt
hello

# Re-open file and search for "hello"
$ led myfile.txt /hello
opened: myfile.txt
   1@ hello
# Append "bye"
: a
   2> bye
# Print the file
: n
   1: hello
   2@ bye

# Save and exit
: wq
backup: myfile.txt~
wrote:  myfile.txt

Programmer example:

$ make
src/main.c:1234:10: fatal error: ‘xyz’ undeclared here

# Jump in to edit the line!
$ led src/main.c 1234

# or
$ led src/main.c /xyz

Installation

Install SWIG.

Install GNU Readline and History support for your system with the development packages.

This is:

• APT package: libreadline-dev

• Homebrew: readline

• Anaconda: readline

led uses a standard Autotools build.

$ git clone [email protected]:j-woz/led.git
$ cd led
$ ./bootstrap
$ ./configure --prefix=[PREFIX] ...
$ make
$ make install

Use ./configure --help for help.

Non-standard libreadline location

If you have libreadline/libhistory in a non-standard location, such as a from-source installation or an Anaconda environment, use something like:

Anaconda

This pattern works for Linux or Mac.

$ C=$HOME/path/to/conda
# or
$ C=$CONDA_PREFIX
$ export CFLAGS="-I$C/include"
$ export LDFLAGS="-L$C/lib -Wl,-rpath -Wl,$C/lib"
$ export LIBS="-lreadline -lhistory"
$ ./configure --prefix=...
$ make install

Mac Homebrew

$ C=/usr/local/opt/readline
$ export CFLAGS="-I$C/include"
$ export LDFLAGS="-L$C/lib"
$ export LIBS="-lhistory -lreadline"
$ ./configure --prefix=...
$ make install

Usage

Key commands

.

Edit file

a

Append text after current line. Uses Readline.

c

Change line interactively with Readline.

d

Delete line

e [FILENAME]

Edit the given file. Use . for interactive prompt. If no filename is given, it reports the current filename. Re-reads the file. If there are unsaved changes to the file, led reports a warning and does nothing.

E [FILENAME]

Edit the given file like e but unconditionally.

f [FILENAME]

Set the current file name. Uses Readline for filename completion. If no argument is given, simply print current file name. If FILENAME is ., get filename from interactive prompt with Readline completion. If the file already exists, led reports a warning and does nothing.

F [FILENAME]

Set current file name like f but unconditionally. Uses Readline for filename completion.

i

Insert text before current line. Uses Readline.

k[X]

Set bookmark X. Can be used to save important places in a file. X must be a single character. Bookmarks can be listed with K or jumped to with '.

k-[X]

Unset bookmark X.

K

Show all marks.

n

Print lines with line numbers

p

Print lines in raw format.

r [FILENAME]

Read given file, appending after current line. Uses Readline for filename completion. Use FILENAME . for interactive prompt. If no argument is given, uses current file.

q

Quit. If there are unsaved changes, led reports a warning and does nothing.

Q

Quit unconditionally without saving.

w [FILENAME]

Write file. If given an argument, writes to that file, and set the current file to that file.

wq

Write and quit.

x

Paste cut buffer

y

Yank (copy) to cut buffer.

Y

Show cut buffer

/[PATTERN]

Search for PATTERN. If PATTERN is omitted, repeats last search.

\[PATTERN]

Reverse search. If PATTERN is omitted, repeats last search.

=

Show current line number, filename, and say if file is modified.

'[X]

Jump to mark X.

_

Evaluate Tcl code and print result. Useful examples:

: _ puts hello
hello
: _ cd ..  # or anywhere
: _ pwd
/home/self/dir
: _ puts $led::text  #  the text buffer, a list of string
: _ puts $led::cln   #  the current line number
: _ set v [ lindex $led::text 123 ]  #  extract a line of text as a variable
: _ a $v  #  append text (similar to the led command `a`)
: _ i $v  #  insert text (similar to the led command `i`)

This could also be used to implement macros and other extension features.

Addressing

Key commands can be prefixed with line addresses: