.TL "" ""

A Tour of the ast Commands and Libraries

.AU "Glenn Fowler" gsf MH HA6163000 2195 2B-134 "gsf@research.att.com"

.MT 4

.H 1 Introduction

The

.I ast

commands and libraries were developed by the

Software Engineering Research Department

.RI ( aka

the Advanced Software [Technology] Department)

at AT&T Bell Laboratories, Murray Hill, NJ.

The strength of

.I ast

is how its individual components

combine to form a cohesive computing environment across UNIX\u\(rg\d

and non-UNIX platforms.

Cohesiveness*

.FS

Footnote test.

.FE

is maintained by well-defined library interfaces for

algorithms upon which the commands are built.

In many cases a library implementation was the driving force behind

command implementations.

.H 1 Motivation

Why should you consider using the

.I ast

software?

After all, many of the commands look like what's already in

.L /bin

and

.LR /usr/local/gnu/bin .

Although there is some replication, there are also some commands you

won't find anywhere else:

.I the

ksh93, nmake, the 3d filesystem, cia, and yeast.

.H 1 Installation

The

.I ast

software installs in a single directory hierarchy, rooted at

.LR $INSTALLROOT ,

usually

.L /usr/local/ast

or

.LR /usr/add-on/ast .

The top level

.L $INSTALLROOT

directories are:

.EX

bin executable binaries and scripts

fun \fIksh93\fP shell functions

lib libraries

lib/\fIcommand\fP related files for \fIcommand\fP

src/cmd/\fIxxx\fP source for command \fIxxx\fP

src/lib/lib\fIxxx\fP source for library \fIxxx\fP

.EE

To access the commands and related data files:

.EX

export PATH=$INSTALLROOT/bin:$PATH

.EE

For each

.I command

that has a related data file

.IR file ,

.I file

is found by searching

.L $PATH

for

.IL "" ../lib/ command / file ,

e.g.,

the magic file for the file command is

.L ../lib/file/magic

on

.LR $PATH .

If

.L $HOME/bin

is before

.L $INSTALLROOT/bin

in

.L $PATH

then you can selectively override standard

.I ast

related files by placing them in the directory

.IL "" $HOME/lib/ command .

This allows executables to be built without hard-coded pathnames and also

requires only a change in

.L $PATH

when

.L $INSTALLROOT

changes.

.P

On systems with shared libraries one of

.EX

export LD_LIBRARY_PATH=$INSTALLROOT/lib:$LD_LIBRARY_PATH

export LIBPATH=$INSTALLROOT/lib:$LIBPATH

export LPATH=$INSTALLROOT/lib:$LPATH

.EE

is required to locate the

.I ast

shared libraries.

.H 1 Exploration

.I tw

combines

.I find

and

.IR xargs .

It provides C style expressions on path names and elements of

.LR "struct stat" .

To find suspicious executables:

.EX

tw -d / -e "uid=='root' && (mode&'u+s') && parent.uid!=uid"

.EE

to change the owner of all of bozo's files:

.EX

tw -d / -e "uid=='bozo'" chown clown:circus

.EE

.I tw

collects file pathname arguments up to the exec arg limit before it

executes the command.

For paranoid users:

.EX

tw chmod go-rwx

.EE

which is equivalent to:

.EX

chmod -R go-rwx

.EE

(Now you don't need to add a

.L -R

option to your favorite commands.)

To find all source files that include

.LR foo.h :

.EX

tw -e "name=='*.[chly]'" grep -l '^#.*include.*["<]foo\.h[>"]'

.EE

.P

.I libast

handles the magic number matching for the

.I file

command.

The magic file,

.LR $INSTALLROOT/lib/file/magic ,

is carefully constructed to give the same output across all architectures:

.EX

cd $HOME/arch

file */bin/cat

.EE

might produce:

.EX

att.i386/bin/cat: elf i386 executable, 32-bit, little-endian, ..

bsd.i386/bin/cat: bsd 386 executable, compact, paged, pure, no..

hp.pa/bin/cat: hp pa-risc executable, shared, dynamically l..

sgi.mips2/bin/cat: elf mips executable, 32-bit, dynamically lin..

sol.sun4/bin/cat: elf sparc executable, 32-bit, dynamically li..

sun4/bin/cat: sun sparc executable, paged, dynamically lin..

.EE

.I tw

uses the same interface, making it easy to search for files based on type,

name and content.

The following searches for executable scripts:

.EX

tw -e "(mode&'+x') && type!=DIR && magic!='*executable*'"

.EE

The

.I tw

algorithm efficiently detects file system loops, so following

symbolic links is not a problem.

The same algorithm is used by all

.I ast

commands that traverse

directory hierarchies,

and the following options to control pathname resolution:

.EX

-L (logical) follow symbolic links

-P (physical) don't follow symbolic links

-H (metaphysical) -L for command line files, -P otherwise

.EE

The

.I ksh93

.I getconf

builtin controls the default traversal mode:

.EX

getconf PATH_RESOLVE - { logical, physical, metaphysical }

.EE

.H 1 Configuration

.H 1 Compression

.H 1 Conclusion