What s the difference between and in Bash

Question

I looked at bash man page and the    says it uses Conditional Expressions  Then I looked at Conditional Expressions section and it lists the same operators as test  and      So I wonder  what is the difference between   and    in Bash

User · Answer

is the same as the test builtin  and works like the test binary  man test    works about the same as   in all the other sh-based shells in many UNIX-like environments only supports a single condition   Multiple tests with the bash  amp  amp  and    operators must be in separate brackets   doesn t natively support a  not  operator   To invert a condition  use a   outside the first bracket to use the shell s facility for inverting command return values     and    are literal string comparisons     is a bash   is bash-specific  though others shells may have implemented similar constructs   Don t expect it in an old-school UNIX sh     and    apply bash pattern matching rules  see  Pattern Matching  in man bash has a    regex match operator allows use of parentheses and the     amp  amp   and    logical operators within the brackets to combine subexpressions    Aside from that  they re pretty similar -- most individual tests work identically between them  things only get interesting when you need to combine different tests with logical AND OR NOT operations

User · Answer

In bash  contrary to       prevents word splitting of variable values

User · Answer

The most important difference will be the clarity of your code  Yes  yes  what s been said above is true  but       brings your code in line with what you would expect in high level languages  especially in regards to AND   amp  amp    OR       and NOT     operators  Thus  when you move between systems and languages you will be able to interpret script faster which makes your life easier  Get the nitty gritty from a good UNIX Linux reference  You may find some of the nitty gritty to be useful in certain circumstances  but you will always appreciate clear code  Which script fragment would you rather read  Even out of context  the first choice is easier to read and understand     if    -d  newDir  amp  amp  -n   echo  newDir   grep     webRootParent     amp  amp  -n   echo  newDir   grep           then       or  if   -d   newDir  -a -n    echo   newDir    grep     webRootParent     -a -n    echo   newDir    grep           then

User · Answer

is bash s improvement to the   command  It has several enhancements that make it a better choice if you write scripts that target bash  My favorites are    It is a syntactical feature of the shell  so it has some special behavior that   doesn t have  You no longer have to quote variables like mad because    handles empty strings and strings with whitespace more intuitively  For example  with   you have to write  if   -f   file      to correctly handle empty strings or file names with spaces in them  With    the quotes are unnecessary   if    -f  file     Because it is a syntactical feature  it lets you use  amp  amp  and    operators for boolean tests and  lt  and  gt  for string comparisons    cannot do this because it is a regular command and   amp  amp        lt   and  gt  are not passed to regular commands as command-line arguments  It has a wonderful    operator for doing regular expression matches  With   you might write  if     answer    y -o   answer    yes     With    you can write this as  if     answer     y es         It even lets you access the captured groups which it stores in BASH REMATCH  For instance    BASH REMATCH 1   would be  es  if you typed a full  yes  above  You get pattern matching aka globbing for free  Maybe you re less strict about how to type yes  Maybe you re okay if the user types y-anything  Got you covered   if     ANSWER   y        Keep in mind that it is a bash extension  so if you are writing sh-compatible scripts then you need to stick with    Make sure you have the    bin bash shebang line for your script if you use double brackets   See also   Bash FAQ -  What is the difference between test    and       Bash Practices - Bash Tests Server Fault - What is the difference between double and single brackets in bash

[bash] What's the difference between [ and [[ in Bash?

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