IFS set to backslash

[Eduardo A . Bustamante López]

I was playing with the following scenario:

IFS set to backslash,
using read (with and without -r),
triggering field splitting by passing multiple names to read,
triggering field splitting by expanding an unquoted parameter.

And, I found the following results:

(note: the ones with a # <something>, that means that the 'read' was fed that
something, via: "$sh" -c 'code that reads' <<< "something")

(note: bbsh is busybox ash, and bsh is heirloom sh)

# -   code [ # input ]                               bash  ksh93  mksh  zsh   
bbsh  bsh   dash  
# 1   IFS=\\ a=\<\\\>; printf %s\\n $a               <^J>  <^J>   <^J>  <^J>  
<^J>  <\>   <^J>  
# 2   IFS=: b=\<:\>; printf %s\\n $b                 <^J>  <^J>   <^J>  <^J>  
<^J>  <^J>  <^J>  
# 3   IFS=\\ read f g; printf %s\\n "$f" # <\>       <>    <      <     <     
<>    <     <>    
# 4   IFS=\\ read f g; printf %s\\n "$f" # <\\>      <\>   <      <     <     
<\>   <     <\>   
# 5   IFS=\\ read f g; printf %s\\n "$f" # <\^J>     <>    <      <>    <     
<>    <>    <>    
# 6   IFS=\\ read f g; printf %s\\n "$g" # <\>             >      >     >       
    >           
# 7   IFS=\\ read f g; printf %s\\n "$g" # <\\>            \>     \>    >       
    >           
# 8   IFS=\\ read f g; printf %s\\n "$g" # <\^J>                                
                
# 9   IFS=\\ read f; printf %s\\n "$f" # <\>         <>    <\>    <\>   <>    
<>    <>    <>    
# 10  IFS=\\ read f; printf %s\\n "$f" # <\\>        <\>   <\\>   <\\>  <\>   
<\>   <\>   <\>   
# 11  IFS=\\ read f; printf %s\\n "$f" # <\^J>       <>    <      <>    <>    
<>    <>    <>    
# 12  IFS=\\ read -r f g; printf %s\\n "$f" # <\>    <     <      <     <     < 
    <     <     
# 13  IFS=\\ read -r f g; printf %s\\n "$f" # <\\>   <     <      <     <     < 
    <     <     
# 14  IFS=\\ read -r f g; printf %s\\n "$f" # <\^J>  <     <      <     <     < 
    <     <     
# 15  IFS=\\ read -r f g; printf %s\\n "$g" # <\>    >     >      >     >     > 
    >     >     
# 16  IFS=\\ read -r f g; printf %s\\n "$g" # <\\>   \>    \>     \>    \>    
\>    >     \>    
# 17  IFS=\\ read -r f g; printf %s\\n "$g" # <\^J>                             
                
# 18  IFS=\\ read -r f; printf %s\\n "$f" # <\>      <\>   <\>    <\>   <\>   
<\>   <\>   <\>   
# 19  IFS=\\ read -r f; printf %s\\n "$f" # <\\>     <\\>  <\\>   <\\>  <\\>  
<\\>  <\\>  <\\>  
# 20  IFS=\\ read -r f; printf %s\\n "$f" # <\^J>    <     <      <     <\    
<\    <     <     


Some comments I have:

- bash and dash seem to:
 * read the input,
 * if -r is not in effect, remove backslashes, except if these are escaped,
 * then they should split the input into fields, but they do not (see: #4)

- ksh93 and mksh behave identically, except for #5 and #11 (I think this is an
  mksh bug). From POSIX, I think the ksh's are wrong in #9 and #10.

The script I used to generate this is attached.

ifs
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