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For example, I have a string "ahfiehfke$jfwfjejf0". Is there an elegant way to drop all characters after "$"? I know loop through and StringDrop till we hit the "$" would work, but I'm wondering if there is a better way.

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    $\begingroup$ First@StringSplit["ahfiehfke$jfw$fje$jf0", "$", 2] $\endgroup$ – Dr. belisarius Apr 28 '15 at 16:09
  • $\begingroup$ @belisarius beat me to it. $\endgroup$ – rcollyer Apr 28 '15 at 16:10
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    $\begingroup$ First[StringCases["ahfiehfke$jfwfjejf0", ___ ~~ "$", 1]] $\endgroup$ – Coolwater Apr 28 '15 at 16:11
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    $\begingroup$ @Coolwater Your version fails when there are more than one $ in the string. The correct version: First[StringCases[str, Shortest[___] ~~ "$", 1]]. $\endgroup$ – Alexey Popkov May 23 '15 at 6:08
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StringTrim["ahfiehfke$jfwfjejf0", "$" ~~ __];

StringDelete["ahfiehfke$jfwfjejf0", "$" ~~ __]; (*V10.1*)
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A bunch of regex methods:

str = "ahfiehfke$jfwfjejf0";

(* Coolwater *)
StringCases[str, RegularExpression["(?s).+?\\$", 1]][[1]]

StringReplace[str, RegularExpression["(?s)\\$.*"] :> "$", 1]

These use look-behind regexes:

StringReplace[str, RegularExpression["(?s)(?<=\\$).+"] :> "", 1]

StringTrim[str, RegularExpression["(?<=\\$).+"]]

(Thanks to Alexey for pointing out the need to properly handle newline characters.)

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  • $\begingroup$ Note that both StringReplace solutions fail if the string contains a newline character \n after "$". You need to add the (?s) option to fix this. $\endgroup$ – Alexey Popkov May 23 '15 at 2:43
  • $\begingroup$ Ah, of course. Thanks @Alexey. $\endgroup$ – J. M.'s ennui♦ May 23 '15 at 2:53
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    $\begingroup$ ... and the StringCases version fails if the string contains a newline character before $: it also needs the (?s) modifier. Only the StringTrim version works correctly without it because for StringTrim this modifier is already switched on internally. $\endgroup$ – Alexey Popkov May 23 '15 at 5:53
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    $\begingroup$ The StringCases version also works incorrectly when there are more than one $ in the string. The correct version: StringCases[str, RegularExpression["(?s).+?\\$"], 1][[1]]. $\endgroup$ – Alexey Popkov May 23 '15 at 6:03
  • $\begingroup$ Ah, that's what I get for trying to answer without a computer. :D Thanks again, @Alexey. $\endgroup$ – J. M.'s ennui♦ May 23 '15 at 6:04
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Another method:

StringTake[str, StringPosition[str, "$", 1][[1, 1]]]

A comparison of performance of different methods which give identical results:

Needs["GeneralUtilities`"]
str = StringJoin@{Table["a", {1000}], Table["ahfieh\nfke$jfw\nfje$jf0", {1000}]};
Replace[Hold[{
     StringTrim[str, "$" ~~ __] <> "$",
     StringDelete[str, "$" ~~ __] <> "$",
     First@StringSplit[str, "$", 2] <> "$",
     First[StringCases[str, Shortest[___] ~~ "$", 1]],
 StringCases[str, RegularExpression["(?s).+?\\$"], 1][[1]],
     StringReplace[str, RegularExpression["(?s)\\$.*"] :> "$", 1],
     StringReplace[str, RegularExpression["(?s)(?<=\\$).+"] :> "", 1],
 StringTrim[str, RegularExpression["(?<=\\$).+"]],
     StringTake[str, StringPosition[str, "$", 1][[1, 1]]]
     }], x_ :> {HoldForm@x, AccurateTiming@x}, {2}] // 
  ReleaseHold // TableForm

table

It seems that the absolute winner is: 

StringReplace[str, RegularExpression["(?s)\\$.*"] :> "$", 1]
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