From 28f631e02bbf7e4cbd763fc74c4941d3f55a030f Mon Sep 17 00:00:00 2001 From: johannst Date: Sat, 19 Sep 2020 13:57:06 +0000 Subject: deploy: 4a5cd61b7c536ecf1bdb288cb6d584c190b1f6c7 --- print.html | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 78 insertions(+), 4 deletions(-) (limited to 'print.html') diff --git a/print.html b/print.html index 3d8d34d..e08e9c0 100644 --- a/print.html +++ b/print.html @@ -355,6 +355,42 @@ command 2>&1 >file
  • duplicate fd 1 to fd 2, effectively redirecting stderr to stdout
  • redirect stdout to file
    • +

    Argument parsing with getopts

    +

    The getopts builtin uses following global variables:

    + +
    getopts <optstring> <param> [<args>]
+
    + +

    Example

    +
    #!/bin/bash
+function parse_args() {
+	while getopts "f:c" PARAM; do
+		case $PARAM in
+			f) echo "GOT -f $OPTARG";;
+			c) echo "GOT -c";;
+			*) echo "ERR: print usage"; exit 1;;
+		esac
+	done
+	# users responsibility to reset OPTIND
+	OPTIND=0
+}
+
+parse_args -f xxx -c
+parse_args -f yyy
+

    Completion

    The complete builtin is used to interact with the completion system.

    complete                    # print currently installed completion handler
@@ -375,7 +411,7 @@ COMPREPLY       # array with possible completions

    The compgen builtin is used to generate possible matches by comparing word against words generated by option.

    -
    compgen [option] [word]
+
    compgen <option> <word>
 
 # usefule options:
 # -W <list>    specify list of possible completions
@@ -390,7 +426,7 @@ compgen -W "foo foobar bar" "f"
 # compare "hom" against file/dir names and generate matches
 compgen -d -f "hom"
 
    
-
    Example
    
+
    Example
    
 
    Skeleton to copy/paste for writing simple completions.
    
 
    Assume a program foo with the following interface:
    
 
    foo -c green|red|blue -s low|high -f <file> -h
@@ -1221,7 +1257,7 @@ major_pagefault: Happens when the page needed is NOT in memory, the kernel
   -l <filter> . show who calls into lib matched by <filter>
   -C .......... demangle
 
    
-
    Example
    
+
    Example
    
 
    List which program/libs call into libstdc++:
    
 
    ltrace -l '*libstdc++*' -C -o ltrace.log ./main
 
    
@@ -1480,7 +1516,7 @@ void run1(int x) {
 
  • run0: bar is on the path without branch
    • 
 
  • run1: foo is on the path without branch
    • 
 
-
    run0:
+
    run0:
         test    edi, edi
         jne     .L4
         xor     eax, eax
@@ -1842,6 +1878,44 @@ LO ADDR
 
    
 
 
+
    ASM skeleton
    
+
    Small assembler skeleton, ready to use with following properties:
    
+
      
+
    • use raw Linux syscalls (man 2 syscall for ABI)
      • 
+
    • no C runtime (crt)
      • 
+
    • gnu assembler gas
      • 
+
    • intel syntax
      • 
+
    
+
    # file: greet.s
+
+    .intel_syntax noprefix
+
+    .section .text, "ax", @progbits
+    .global _start
+_start:
+    mov rdi, 1                      # fd
+    lea rsi, [rip + greeting]       # buf
+    mov rdx, [rip + greeting_len]   # count
+    mov rax, 1                      # write(2) syscall nr
+    syscall
+
+    mov rdi, 0                      # exit code
+    mov rax, 1                      # exit(2) syscall nr
+    syscall
+
+    .section .rdonly, "a", @progbits
+greeting:
+    .asciz "Hi ASM-World!\n"
+greeting_len:
+    .int .-greeting
+
    
+
    
+
    Syscall numbers are defined in /usr/include/asm/unistd.h.
    
+
    
+
    To compile and run:
    
+
    > gcc -o greet greet.s -nostartfiles -nostdlib && ./greet
+Hi ASM-World!
+
    
 
    References