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hexec - Online in the Cloud

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This is the command hexec that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator

PROGRAM:

NAME


hexec - a process execution hooking tool

SYNOPSIS


hexec <OPTIONS> [expr] [cmd] [args...]

DESCRIPTION


hexec is a tool to hook into process exececution calls (exec family of syscalls). You can
define an expression that is executed against any hooked exec call. This expression may
also contain a replacement exec call.

OPTIONS SUMMARY


Here is a summary of the options to hexec.

--help | -h Print a options/expr summary page
--version | -v Print hexec version
--log-out | -lo set output file for error and -print output

OPTIONS


-h Print a options/expr summary page

--help Print a options/expr summary page

-lo Set the output file for error and -print output. This can be required if writing
to stderr could cause malfunction because some processes read from stderr and
expect a well defined output.

EXPRESSIONS


The expression is executed against all process execution calls. If the expression returns
true, the original call is skipped.

<expr> -and <expr>

<expr> -a <expr>

<expr> <expr>
Returns true if both expressions return true. If the left returns false, the right
expression is never executed.

<expr> -or <expr>

<expr> -o <expr>
Returns true if one of both expressions returns true. If the left returns true, the
right expression is never executed.

-path <pattern>
Returns true if the path of the executable matches <pattern>. <pattern> is a bash
compatible wild card pattern.

-ipath <pattern>
Same as -path, but case insensitive.

-name <pattern>
Returns true if the base name of the executable matches <pattern>. <pattern> is a
bash compatible wild card pattern.

-iname <pattern>
Same as -name, but case insensitive.

-contains <str>
Returns true if the path of the executable containes the string <str>.

-icontains <str>
Same as -contains, but case insensitive.

-print Print all arguments to the called process. Returns always true.

-exec <cmd> [args...] ;
Executes <cmd> with [args...] as arguments. This expression must be terminated with
a semicolon. You can use argument placeholders in <cmd> and [args...] (see below).
This expression always returns true.
NOTE: Please be aware that you may need to escape or quote the terminating
semicolon to not confuse your shell.

-sh <script>
Interprets <script> as a shell script by invoking /bin/sh with the arguments -c
'<script>'. You can use argument placeholders inside <script>. Please note that -sh
only expects a single argument and not a variable list of arguments (as -exec
does). Using -sh is the same as using -exec sh -c <script>.

PLACEHOLDERS FOR -exec EXPRESSION


Every -exec expression can use placeholders in the argument list to obtain information
from the original exec call. Each placeholder starts with { and ends with }. Use \{ if you
want to use a { in your argument list. The placeholders are replaced when the -exec
expression is evaluated.

Placeholder types:

{n} Will be replaced with the number of arguments in the original call.

{<idx>}
Will be replaced with the original argument at index <idx>. Example: {1} would give
the first argument. You can prepend <idx> with placeholder flags.

{} Will be replaced with all arguments from the original call. Each argument is
seperated with a space. You can use placeholder flags.

NOTE: The executable name is also considered as argument. This means that a call like
"echo test" will result in two arguments, "echo" and "test".

PLACEHOLDER FLAGS


s Every argument is inserted as single argument instead of concatenating all
arguments.
Consider the arguments 'a', 'b' and 'c'. Without s, -exec {} \; would result in
-exec 'a b c' \;, which in many cases is not what you want. -exec {s} \; howewer
would result in -exec 'a' 'b' 'c' \;.

q Quote every single argument.

e Escape all non alpha-numeric characters. This flag is very useful when using a "sh
-c <...>" in the -exec expression.

Examples

-exec echo {} \; with the call 'a' 'b' 'c'
results in: 'echo' 'a b c'

-exec echo {q} \; with the call 'a' 'b' 'c'
results in: 'echo' 'a' 'b' 'c'

-exec sh -c 'echo {}; {}' \; with the call 'sh' '-c' 'gcc d.c >> log.txt'
results in: 'sh' '-c' 'echo sh -c gcc d.c >> log.txt; sh -c gcc d.c >> log.txt'
Please note that this will not do what you may expect, as the >> is handled wrong
in this case.

-exec sh -c 'echo {e}; {}' \; with the call 'sh' '-c' 'gcc d.c >> log.txt'
results in: 'sh' '-c' 'echo sh \-c gcc\ d\.c\ \>\>\ log\.txt; sh -c gcc d.c >>
log.txt'

CHANGES TO PROCESSES


hexec will add some environment variables to the hooked processes. These are (may not be
complete):

LD_PRELOAD
hexec adds libhexec-hook.so to the list of preloaded libraries.

HEXEC_EXPR_SHM
Contains the name of the internal shared memory object.

HEXEC_LOG_FD
Contains the file descriptor for error and -print output.

Please do never modify these environment variables. Also take care when you use these
variables, because the name and content of the variables may change in the future.

EXAMPLES


hexec -name 'gcc' -exec ccache {s} \; make
Calls make, which will then call gcc several times. The executable name of each
hooked process execution is tested against the file pattern "gcc" and "ccache {s}"
is called each time a match is found. '{s}' will be replaced with the original (the
hooked) call. In this example, a call to "gcc -o test.o test.c" would be replaced
with "ccache gcc -o test.o test.c"

HOW IT WORKS


TODO

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